Abstract: To solve the control rod position sensor measurement problems in Tianwan nuclear power plant,the requirement of detective device for the control rod position sensor was proposed.In this paper,the design scheme and its technological process was completed based on the structure features and function requirements of the step-type control rod position sensor device,and the vessel simulating the working conditions,the pressure loop,the heating device and the control system were designed.The electric heating power,and the proportion,integral,differential setting parameters and pressure parameter of the control system were verified by the tests of heat capacity,automatic temperature control,and the pressure following control.Tests show that the function of each unit is normal.