Research on the effect of main spindle deformation which is caused by hobbing force of gear hobbing machine is an important way to diminish or control the machining tolerance of gear. This paper bases on the structure and technique parameter of some typical large-scale NC gear hobbing machine, and the theory of bend and deformation of beam, a novel equation was proposed in this paper to calculate the hobbing force and deformation by practical hobbing parameter. By calculating and analyzing gear hobbing force and deformation data, we can conclude a change rule between hobbing force and deformation with spindle rotative velocity and hobbing depth. And we can reach a conclusion that we should increase hob rotative velocity and feed in a small hobbing depth in several times, it will diminish cutting force, deformation of hob and workpiece spindle, which will improve the machining precision, efficiency and diminish product scrap ratio. It also prove this research approach has reference value for optimizing gear hobbingmachine structure design, choice of processing technique parameter and machining error prediction and compensation.