In order to investigate effect of nonlinearity in rolling bearing on cycloidal drive transmission efficiency,a novel estimation method for transmission efficiency was proposed by incorporating the structural parameters,contact load and bearing parameters of cycloidal drive.Elasticity of rolling bearing between input shaft and cycloid disk was described as stiffness model with nonlinear parameters.By analyzing action of bearing force,inertial force and contact load,dynamic formulation of cycloidal disk was established as differential equation with variable coefficient based on the Newton method.The elastic displacement of the bearing was obtained by solving the equation,and was introduced in the transmission efficiency model with bearing stiffness parameters.The transmission efficiency under different bearing stiffness parameters and operating conditions was compared and analyzed.Iterative calculation was utilized to determine accurate bearing parameters,which were modified repeatedly until theoretical efficiency was close to the tested ones.Results show that the transmission efficiency is insignificantly affected by the running speed and load when the bearing stiffness exponent is smaller,while the transmission efficiency increases with the increase of the load when the bearing stiffness exponent is larger.The proposed bearing stiffness model has a synthetic effect and leads to consistent transmission efficiency with the test ones.This works provides efficient and accurate theoretical methods for efficiency evaluation of cycloidal drive.