The invention relates to the technical field of lithium battery package equipment, in particular to a mounting device of a lithium battery cap. The mounting device comprises a workbench, an air cylinder, a turntable bracket, a stepping motor and a heater, wherein a support plate is mounted on the side face of the workbench; the air cylinder is mounted on an air cylinder saddle; an upper press moldis mounted on an air cylinder push rod of the air cylinder; an annular groove is formed in the turntable bracket; the turntable bracket is rotationally connected with a turntable via the annular groove; lower press molds are uniformly arranged at the periphery of the turntable; the stepping motor is located in the turntable bracket; a driving shaft of the stepping motor penetrates through the turntable bracket and is connected with the turntable; a crease-resistant structure is arranged on the upper press mold; fixed ring sleeves and emergency stop devices are mounted on the lower press molds; the emergency stop devices are in series connection to a power supply circuit of the air cylinder; and the heater is mounted in the upper press mold and connected to the power supply circuit. The device is simplified in structure and high in production efficiency and can effectively reduce damages to a battery cap component during mold assembly; and the quality reliability of the cap is high.