In order to measure the tiny pressure variation in the harsh environments,a high precision and cantilever beam fiber pressure measurement system based on heterodyne Doppler principle was presented.Through analyzing the relationships of the pressure variation,the deformation of the cantilever beam,the Doppler frequency shift and the output voltage in the optical fiber pressure measurement system,the mathematical model was established.Based on differential Doppler measurement principle,the deformation of cantilever beam could be measured quickly and accurately to realize the displacement measurement at the nanometer scale.The reflector is moved from the middle of the cantilever beam to its free end,which improves the sensitivity of the measurement.With optical fiber collimator instead of traditional fiber,the parallelism of the light beam is higher,and the divergence angle is smaller,which improves the accuracy of the measurement.Sampling integrator is selected to extract effective signal,and combined with the software,weak signals are extracted in strong noise signals,which improves the signal-to-noise of the system.Experimental results show that the uncertainty of the fiber pressure measurement system is less than 0.05%,and it can realize the measurement of tiny and slow pressure variation.This system is suitable for petroleum and chemical industry.