A manhole cover disassembly and assembly device for a heat exchanger belongs to the technical field of manhole cover disassembly and assembly. The present invention solves the disassembly difficulty due to large weight of the manhole cover and damage other parts in the disassembly process. The device includes a fixed plate, a connecting rod, a tube sleeve, a wrench and lifting plate. The fixed plate is mounted on the manhole cover; the curved portion of the connecting rod is connected to a trapezoid lock catch; the lower end of the trapezoid lock catch is provided with support legs; the curved portion of the connecting rod is connected to the fixed plate via a pin roll; the other end of the connecting rod is provided with a wrench; lifting plate is fixedly welded on the tube sleeve; the tube sleeve is formed with a groove; the tube sleeve sleeves over the connecting rod; the groove of the tube sleeve and the set screws on the connecting rod cooperate for installation. The device has simple structure, few process steps, easy dismounting, safety and reliability, and greatly reduces the disassembly cycle of manhole cover.