I have changed rail pressure switch on bmw 530 diesel but when car is cold start if engine is hot the car not start until i spray easy start into it

Reputedly a Renault engine and reckoned to be one of the best small diesels. It isn't a good idea to use an ether spray regularly.

The reasons why a diesel doesn't start and from your description doesn't even start when hot (?), can be many from poor compressions, low cranking speed, preheat not working, bad injector spray patterns or even the high pressure pump being slow to raise the main fuel rail pressure to the required level.

The common rail diesel has electric injectors controlled by computer and if the fuel pressure isn't raised to that required in the expected time the computer will not begin injection so perhaps that is the trouble, using easy start will make the engine turn faster perhaps overcoming the problem.
I wonder if it starts with a tow without the ether...

Once what can be checked has been checked and repaired if necessary, the high pressure side will need expert attention with some good diagnostic equipment.

I would suspect vapor lock. The fuel rails are getting hot and it turns the diesel into a vapor instead of a liquid. A liquid is what is needed to go into the injectors. Try insulating all of the fuel lines with the shiny side out to reflect heat back to the engine.

Has the fuel pressure regulator been checked?

Check the cam position sensor and crank pposition sensor- they will test like a tansistor, because they are a hall effect transistor. I suspect one of those two sensors may be at fault.

We do not have BMW diesels (thank goodness) in the USA. That said has the engine control moule been scanned for fault codes? You must do this 1st.

BMW 330 330i 1999 2005 Repair Service Manual PDF
Here's this link from where you can get step wise instructions on how to fix it sir

Dear sir , Hyundai verna fault code p1186 we check found warring and couplers was ok and we replace injector and fuel rail problem was not resolved, cold starting engine vavrection and rpm stack and white smoke and hot conduction normal but rung conduction engine vavrection and missing no accelerator is working please suggest

Glow plugs are heating devices to aid starting diesel vehicles.
Purpose:Diesel engines, unlike petrol engines, do not use spark plugs to induce combustion. Instead, they rely solely on compression to raise the temperature of the air to a point where the diesel will combust spontaneously when introduced to the hot high pressure air. The high pressure and spray pattern of the diesel ensures a controlled, complete burn. The piston rises, compressing the air in the cylinder; this causes the air's temperature to rise. By the time the piston reaches the top of its travel path, the temperature in the cylinder is very high. The fuel mist is then sprayed into the cylinder; it instantly combusts, forcing the piston downwards, thus generating power. The pressure required to heat the air to that temperature, however, necessitates the use of a large and very strong engine block. The problem posed is that in cold weather, if the engine has not been running (as is the case when the car is left to sit overnight), that the large engine block becomes very cold; when one then attempts to start the engine, the cold engine block acts as a heat sink, quickly dissipating the heat generated by the pistons compressing air. The engine is then unable to start, because it cannot generate and maintain enough heat for the fuel to ignite. For that reason indirect injected diesel engines are manufactured with glow-plugs in each prechamber, and direct injected diesel engines are manufactured with glow-plugs in each combustion chamber.

Wikipedia

Try turning the ignition on (not to turn the engine over but only on) for 5 seconds and then off then repeat that three or four times then try and start it. If it starts up immediately after that then you have a fuel pressure problem and by doing this you are priming up the high pressure fuel rail. possible causes are a fuel filter blockage, if you dont know the history of the fuel filter then replace it, or could be a pump issue or a pressure regulator on the rail issue.

if you have the same problem with the engine Hot or Cold then it may be the cold start fuel injector in the throttle body / carb. may need to be cleaned or replaced.
may be chock and linkage

you could have a couple differnet issues. cold start misfires, an intake air leak, poor compression with engine cold,or a fuel pressure issue with a leaking injector or fuel pressure is bleeding back due to a faulty pressure regulator. my recommendation is to buy a fuel pressure gauge and monitor pressure overnight. you could also pull the fuel rail and see if an injector is leaking at the same time. you can spray the intake system with a highly volitile liquid(with engine running) to see if idle speed changes to check for an air leak