The work aims to solve the problem that the varistor has fine pinning of the product in the process of encapsulating the insulating layer of the automatic encapsulator, improve the encapsulation quality of the product and the automation level of the encapsulation process, and reduce the labor cost. Firstly, the encapsulation mode of the traditional encapsulation process and the automatic encapsulation production line were compared, the reasons why the automatic encapsulation machine causes the pinning of the product package were analyzed, and then a solution to the problem solution was proposed. Finally, the Mitsubishi FX3U-60MT series PLC was used as the control core component to rationally design the enveloper. The control system had simple structure, convenient operation and strong programmability, which solved the problem of fine pinning of product encapsulation pins in encapsulation process. The control system has high reliability and maintainability. It improves the quality and efficiency of varistor insulation layer encapsulation, and improves the intelligence and automation level of the encapsulation machine.