My car is building gas when I open the gas tank it releases the gas, I know all about purge system and I have tried different cap and also different vapor canister too but problem still insists, for some weird reason there is no EVAP sensor in gas tank.
TL DR: Most likely this is not an issue, but rather the EVAP system at work.
Every emissions controlled vehicle has an EVAP system which controls the amount of fuel which is exhausted to the atmosphere from the fuel system/tank. The EVAP system can test itself one of two ways, either through pressure in the tank or vacuum. Either pressure or vacuum will cause a pressure release sound as you open the fuel cap. If pressure is present, it can escape through a whoosh type sound. If vacuum is present, atmosphere can escape into the fuel tank through a whoosh type sound. It's very hard to distinguish between the two unless you know how your EVAP system works.
If there was an issue with the EVAP system, the system itself will let you know through a check engine light. My suggestion to you is to fill the tank to nearly full (between 3/4 and 7/8 full) and see if things decrease any. I really don't believe you have a real issue.