giving 5 degree tilt to gy-80, power off the system , after few seconds we start the system our prg/ sensor reads 0 degrees whereas it should read 5 degrees plz help



I am not familiar with the device, but it sounds like the sensor is taking the value at startup to be zero degrees. That is certainly what happens with the sensors in my multi-rotors which must be level when the battery is connected so that the sensors have a valid zero reference.

You could consider saving the angle at shutdown to EEPROM but that would require a proper shutdown sequence to be initiated rather than just pulling the plug.