In order to improve the security in pipes inspection for in-pipe robots, the current study developed an electromagnetic clutch, which was aimed to insure the in-pipe robots quitting from pipes where they worked in any conditions. The specific size that is 42mm in diameter and 220mm in length was designed for using in pipes. With this contact structure, it still can transfer a relative large torque and hold a 10mm effective distance. After the structure and work principle of the electromagnetic clutch were introduced, the magnetic circuit was analyzed, and then the heat of coils was calculated. The relationship between the attraction and the air distance was worked out based on the Langrage-Maxwell Equations. To testify the correctness of the theory results obtained above, some simulations were made. The data from the simulation also optimized the length of the stopper. Base on the theory result, a prototype was designed and some related experiments were made.