Abstract. Pressure balance workover is an advanced downhole operation technique. It can hoist the strings of the tube or put it down under certain pressure. The research on pressure balance workover rig has become a hotspot in both domestic and overseas. Pressure balance workover operation technique has been widely used oversea. At the present time, relevant studies have been developed in China. In this paper, domestic and international technology status is fully analyzed, working principle of hydraulic lifting system is studied, then equivalent calculation model and calculation method of hoist force are put forward, calculation program of hoist force was compiled for the different oil pipe depth, curve and charts changing with the oil pipe depth are given, It provides a theory reference to field operation.