The Turning-Milling may machine various complex components in once positioning and fixture with the C axis function (revolving milling). But, the vibration phenomenon of workpiece will be aggravating whether C axis is performing static cutting or continuous rotation feeding. A double-motor anti-backlash theory was applied to C axis dividing apparatus to improve the positioning and indexing accuracy of heavy NC turning-milling in this paper. The model of double-motor servo driving system with backlash was set up with mechanism analytic method. The simulation of double-motor anti-backlash was carried out. The simulation results show that the double-motor system with offset voltage has favorable performance to decrease the influence of the backlash non-linearity to the system, can guarantee the system tracks the input parameter stably, and improve dynamic feeding performance in C axis at low speed revolving. And the plant test results show that the accuracy of C axis meet practical demand.