By using a C type induction heater with variable radius and three dimensional tooling car,an electromagnetic induction heating device which is suitable for the preheating of the inner wall surfacing of the nuclear pressurizer and the hydrogen baking is designed in this article. The C induction heater with adjustable radius can heat the large area in a certain range,and the tooling car can adjust the position of the C induction heater in the three-dimensional space. The device is featured by high automation and good heating effect,and is of high engineering application value.