Aiming at the difficulty of accurate monitoring of the discharge pressure of rotary vane compressor, a method of sensing the discharge pressure of rotary vane compressor based on fiber Bragg grating (FBG) improved relief valve was proposed. Firstly, according to the structural characteristics of the pressure relief valve of the rotary vane compressor and the FBG sensing theory, the model of the diaphragm pressure sensor was established, and the mapping relationship between the pressure and the central wavelength was revealed. Secondly, a three-stage FBG pressure temperature composite sensor based on pressure relief valve was designed. Theoretical analysis shows that the sensitivity of the sensor is 304. 26 pm/ MPa. Finally, through simulation experiment analysis, the influence of diaphragm radius and thickness on sensor sensitivity was studied, and the optimal combination of radius and thickness (R = 5 mm, h = 0. 6 mm) was obtained. The experimental sensitivity is 330. 78 pm/ MPa. The research has important theoretical and practical engineering value for rotary vane compressor condition monitoring and power consumption control.