High reduction ratio can be realized by the two-stage cycloidal pinwheel mechanism with compact structure. In order to evaluate the transmission performance

a special tooth profile design formula for cycloidal tooth profile is built for new two-stage cycloidal drive in this study. Tooth profile equations of two cycloidal gear are transformed into identical coordinate system and used to form expression describing mesh process between cycloidal gear and pins. Thus

the whole tooth contact equations are innovatively proposed based on unloaded tooth contact analysis method

and solved to obtain transmission error. Using different modification values and several profile modification methods

transmission errors of two-stage cycloidal pinwheel mechanism are calculated for comparative analysis. Results indicate that transmission error is relatively smaller in the case of compound modification than single modification

and the smallest in the case of compound modification

i.e. positive equidistance plus positive displacement. The proposed method can provide a theoretical basis for evaluating transmission performance of the new two-stage cycloidal pinwheel mechanism.