Abstract: In celiac minimally invasive robotic laparoscope surgery (MILS), motion interference of two manipulators should be avoided during cooperative operation, such as suturing and knotting operation. A reasonable operation space for two instrument manipulators is given by preoperative positioning analysis. Firstly, the maximum distance index between the two manipulators is selected as the objective optimization function of the gradient projection algorithm. And a closed-form inverse solution of the manipulators is used to improve the algorithm, which can eliminate the cumulative error existed in the inverse kinematics solving process of the gradient projection algorithm. At last, the improved gradient projection algorithm is applied to the preoperative positioning analysis of the celiac minimally invasive surgical robot system. The simulation results show that the improved method can satisfy the preoperative positioning requirements of the surgery system.