The invention discloses a self-adjusting opening and closing hot cover and a full-automatic gene amplification instrument using the hot cover. An existing gene amplification instrument adopts a manualuncovering mode, and the provided pressure varies from person to person, so that the gene amplification effect is influenced. The hot cover comprises a driving mechanism and a hot cover module, wherein the hot cover module comprises a hollow hinged frame, a supporting block, a guide sleeve, a sliding rod, a movable pressing plate, coil springs, a hot cover shell and an annular rubber pad. According to the invention, in a closing process of the hot cover shell, a crank and a connecting rod are driven through a stepping motor, then the connecting rod drives the movable pressing plate, finally the closing process is achieved through acting force of the springs, and it is guaranteed that constant pressing force is kept in the closing process of the hot cover shell under the action of the springs; and the coil springs wound at the two ends can provide constant acting force for the movable pressing plate, so that it is guaranteed that the pressing force of the movable pressing plate on a PCR tube is constant, PCR tubes of 0.1 ml and 0.2 ml can be adapted at the same time, the operation is automatically completed, and after the pressing force of the movable pressing plate on the PCR tubeis pre-adjusted, PCR tube pressing cracking caused by overpressure can be avoided.