Abstract: An ultrasonic automatic inspection robot for nuclear power plant pressure vessel nozzle safe ends was developed and its various components, including mechanical structure, gas circuit design, electronic control and so on were researched. The design principle and design method of implement configurations belonging to the inspection equipment were described. Through optimizing the pneumatic design, the inspection equipment is able to realize several functions, including fix position force maintaining while gas input being break, probes pressing weld with a constant force, and the calibration of test block extension. Control system sends signals to performing machine and receives feedback signals from sensors, and realizes automatic scan at last.