In order to ensure the safety of active satellite, it is necessary to perform an orbit maneuver before the collision between space debris and satellite to protect satellite from space debris. The strategy of continuous-thrust is chosen for avoiding collision. The collision avoidance process is converted to optimal control problem with complicated constraints, while Gauss pseudospectral method is used to solve this problem and the result meets the requirements of avoidance. The simulation results show that the new method can decrease the consumption of fuel. It is significant for avoiding collision between space debris and the satellite.