Taking a RV cycloid planetary reducer used in the excavator as study object. The contact stress theory is adapted to analyze the fatigue strength between the flank of cycloids and pins. The analysis result indicates that the fatigue damage is easy to appear in the root of the cycloid gear. The finite element method is used to quantitative strain and stress analysis between cycloids and pins. The result is consistent to theoretical analysis. The maximum stress is 735. 65 MPa,which is less than the material minimum allowable contact stress.The maximum strain appears at the bearing hole of support crankshaft of the cycloid. Consider that the cycloids and pins are made of GCr15. The analysis of contact fatigue S-N curve of the material GCr15 indicates that there is no contact fatigue failure in the meshing process of the cycloid-pin reducer mechanism.