In order to realize column clamping of fresh tea in tea leaf and stalk separation, a self-locking gripper consisted of slider-crank mechanism and RRR assur group was designed. Analysis showed that, retraction phenomenon might happen if parameters were not suitably selected, which make it difficult to grip small diameter objects. However, it could be avoided by the constraining of retraction height. Secondly, relations between parameters were deduced, based on which an appropriate method was proposed on the determination of design parameters. The design problem was attributed to a transcendental equation, which was solved by particle swarm optimization method. Experimental results showed that grippers designed with this method can realize clamping and self-locking successfully, and a clamping length of 5~15mm was suitable.