In order to study the lubrication characteristics of cycloid drives under grease lubrication，a thermal elastohydrodynamic grease lubrication line contact model was developed for the cycloid drives with Ostwald fluid.The effect of four profile modification methods on lubrication performance was investigated,including negative radial-moving scheme,positive equidistant scheme,combined positive equidistant and positive radial-moving scheme and combined negative equidistant and negative radial-moving scheme.The minimum film thickness,friction coefficient,friction power loss in the meshing period and the total rolling power loss for the whole meshing process were used to evaluate the contact performance of a cycloid drive.Results show that at a certain manufacturing accuracy,the combined positive equidistant and positive radial-moving scheme has the largest minimum film thickness,the smallest friction coefficient and friction power loss and the total rolling power loss for the whole meshing process.The combined positive equidistant and positive radial-moving scheme has the best lubrication performance,while the combined negative equidistant and negative radial-moving scheme has the worst lubrication performance,and the single positive equidistant scheme has better lubrication performance than single negative radial-moving scheme.As the modification value increases,the total rolling power loss for the whole meshing process increases,which represents a worse lubrication performance.As the speed increases,the minimum film thickness in meshing process increases,the friction coefficient decreases,and the friction power loss in the meshing period and the total rolling power loss for the whole meshing process increase.