Traditional path planning methods of a free-floating space robot cause severe disturbance to the base satellite. To solve this problem, a path planning method based on the parameterization of control variables is proposed. This method transforms the path planning problem into an optimal control problem using minimum base posture disturbance as an objective function along with a series of constraints. The control variable parameterization method is used to discretize the problem, and the optimal control problem is transformed into a nonlinear programming problem. In addition, a complete theoretical convergence proof is provided. Thus, the optimal path of the end effector of the free-floating space robot can be accurately estimated. The simulation results indicate that the attitude disturbance of the base satellite caused by the motion path of the proposed method is 0.104 rad, which is 17.53% lower than that of the traditional method of decomposition acceleration, which verifies the effectiveness and optimality of the proposed path planning method.