Abstract: Globoidal indexing cam mechanism with steel balls works under the preload state,its transform function is changed by preloading,and the preload magnitude decides the force of preload.For the cams with single arc raceway and double arc raceway,the pressure angle is analyzed after preloading by adjusting the center distance and increasing the steel ball diameter.The theory of Hertz contact,bending deformation of the shaft and radial elastic deformation of the bearing are used to analyze the relationship between the adjustment of center distance,the increasement of steel ball diameter and elastic deformation of the mechanism,and contact force.Calculation shows that the relationship between the preload force and adjusting magnitude is non-linear,preload forces of all steel balls meshing together are different and change with the cam angle.The analysis is meaningful for the installation,design and manufacture of the mechanism.