Abstract: When the surgeon performs the master-slave minimally invasive surgery by controlling the force reflection manipulator of the minimally invasive surgical robot, the gravities of its links will impede the manipulation performance. To solve this problem, the gravity torques on the joints of the force reflection manipulator are derived based on the virtual displacement principle, and the correctness of the formulation is verified through Adams simulation. The proposed method is applicable to the robot manipulators with the open-loop and closed-loop structures, and is simpler and more effective than the traditional Newton-Euler method and Lagrange method because it needn't consider the speed and acceleration. Then the link gravities of the force reflection manipulator are compensated fully through motor driving. Experimental results show that the active gravity compensation algorithm based on virtual displacement principle can achieve good performance by reducing the gravity torque effects by 60%, and improve the manipulation performance of the force reflection manipulator.