Based on momentum conservation,the impact issues of space manipulator during capture operation were analyzed,and the concept of "straightarm capture" and "generalized straightarm capture" was proposed.The manipulator configuration,which can meet the requirement on the centroid of base and system,and on endeffector in a line was derived,and the corresponding angular relationship was obtained.The manipulator preimpact configuration that satisfied the above relationship can reduce the effect of impact force on system’s angular momentum,and avoid the limit of joint and torque when controlling the compound.The simulation show the effectiveness of the method.