The grinding force curve always varied as convex in the surface grinding hardening thin workpiece. The workpiece became concavity on the ground profile. Through coupled thermal-mechanical FEM analysis, the variation of grinding magnitude caused by the grinding deformation was the main reason for grinding force variation. The mode of workpiece clamping exerted tremendous influence on the deformation. The grinding force variation affected the heat flux into the workpiece and the grinding temperature. As a result, the grinding depth is non-uniform. Through the relationship among the grinding force, grinding temperature and the grinding thermal deformation，the grinding force can be divided into intervals and be iterated. The predictable grinding force curve has good agreement with the experiment result and is useful to analyze the grinding hardening depth distribution. 