The stateofart of the ultrasonic detection technology and related domestic and foreign engineering technical data are described and the detection system of shield cutter wearing is presented, so as to accurately detect the cutter wearing, determine the cutter replacement time, save the cutter cost and ensure the tunneling safety. Cutter wearing detection devices are installed and debugged and laboratory tests are made. Conclusions drawn are as follows: 1) The detector developed has RS485 communication mode and realtime display function, and, due to the application of the electric conduction link, the problem of measurement line twisting during shield boring is solved; 2) The new type of ultrasonic detector can detect the accurate wearing of the cutter in real time in environment with vibration and temperature, and the detector has good system stability. 