The main winch of rotary drilling rig is mounted on the platform or the lower part of the drilling mast. Effects of mount position of the main winch on the drilling mast hydraulic cylinder load are discussed in the present article. Based on forces on the body of the drilling mast luffing mechanism,and the torque equilibrium around the hinge between the drilling mast and the triangle,a mathematic model of the drilling mast hydraulic cylinder load was established when the main winch was mounted on the platform,and another mathematic model of the drilling mast hydraulic cylinder load with the main winch mounted on the lower part of the drilling mast was also developed by simplifying the mathematic model with the main winch mounted on the platform. A simulation model was built up and analyzed in Matlab software. The results show that the drilling mast hydraulic cylinder load with the main winch mounted on the platform is relatively larger than that on the lower part of the drilling mast,the former is influenced by the lift-arm angle,and compared with the latter,the former exhibits relatively good stability. At last,the simulated results with the main winch mounted on the platform are testified by the experimental data.