The trajectory control tool of high build-up rate well-bore, is such a kind of down hole tool that is used to control the well-bore trajectory of the extended reach well. Due to the complex working environment, so it is necessary to design a special electromagnetic clutch. Firstly we should analysis the hostile working environment of the special electromagnetic clutch. The slipping toothed electromagnetic clutch is selected and structural design is going on to adapt the hostile working environment. In order to meet requirements of meshing when the axis is turning, armature ring gear has been designed specially. The reliability of the design also has been checked and it is proved that such kind of design can meet requirements of working under the hostile environment.