As the water and slurry leakage in shield tail sealing system is of great danger, the shield tail sealing quality test is carried out. The fiber Bragg grating (FBG) pressure monitoring system is set up on the sealing performance test platform of tail brush to continuously measure the pressure of grease cavity at multiple points. The leakage caused by the actual working condition is simulated by opening ball valve of grease cavity under different pressure levels. The experimental results show that: (1) When a certain point of the grease cavity leaks, a slow pressure drop occurs simultaneously in the circumferential direction of the whole grease cavity; the longest time of pressure drop reaches 6 min, and the maximum pressure drop reaches 0. 075 MPa. (2) The pressure variation in the grease cavity during the leakage experiment can be accurately monitored by the system. The monitoring method can provide a feasible solution for the early warning of leakage of shield tail sealing system.