The thick walled vessel uesed in petrochemistry such as hydrogenation reactor is applied in high temperature,high pressure as well as near hydrogen condition.The vessel's inner welding cladding may spall after many years application.A set of auto ultrasonic testing and imaging system for the vessels inner welding cladding spalling was designed,mainly including three parts:the mechanism scanning equipment,the control system and the ultrasonic testing and imaging system.The functions of each part were detailed introduced.In the actual application,good testingeffect,high testing efficiency and reliable testing quality are obtained.