The research object is a force bilateral servo system in which the master side is a hydraulic manipulator and the slave side is a hydraulic cylinder actuated robot. Facing the concussion problem occurred when the slave hand contact rigidity object, a strategy-switching algorithm was proposed. A four-channel slave driving strategy was used to the flexible load and a three-channel strategy without slave force was used to the rigidity load. The switch was judged by the ratio of slave force and velocity. It is proved by the experiments that the strategy is valid and the concussion problem of the former strategy when catching rigidity object could be avoided.