In the automated high-throughput nucleic acid detection system, we need to grip and transfer consumables frequently when carrying out multichannel nucleic acid detection. In order to ensure the efficiency of experiments and solve problems of the deflection and drop when transferring microplates, we design a self-locking mechanical gripper which consists of a rotary positioning module and a gripping module. The absolute position encoder fixed on the top of the stepper motor can collect the position data of the mechanical gripper in real time and send them to the master control board based on STM32 for processing, which ensures the accuracy of the movement of the mechanical gripper. We used SolidWorks to build models of the mechanical gripper and different microplates, and we carried on finite element analysis of microplates to find the suitable gripping position. Through the force analysis, we obtained the pressure distribution and the deformation of different microplates, and defined the effective gripping areas, which is important to the grip and transfer of microplates.