In order to reduce the error of the workpiece outline and improve the machining accuracy, the relationship between curvatureradius and grinding force was researched. Based on the outline feature of these parts, the dynamic arc length and the dynamics model of single particle，the grinding force model of noncircular parts was constructed. As an example, the cam grinding force model was calculated and analyzed. The result shows that the noncircular parts grinding force increases with increasing the radius of curvature if other factors in the grinding process is not cosidered.