Abstract: Based on the force analysis between the standard cycloid gear and pin in the two-difference cycloid drives，the initial clearance between the cycloid disk，which its tooth profile has been modified，and pin can be calculated by means of analytic method．A more accurate force analysis theory about the two-tooth-difference cycloid gearing is carried out．The calculating results are in accord with the engineering practice．

Key words: Force analysis, Initial clearance, Two-tooth-difference cycloid gearing