In chip manufacturing process, the mechanical stress has a great influence on common-emitter current gain β of vertical NPN. By slotting on metal 2, the value of β rebounded. A compressive stress layer of Si3N4 was added into the IMD between metal 1 and metal 2, and the β of the largest NPN had returned to normal mode. At the same time, the β of the other size NPN and PNP still increased. The influence mechanism of stress was analyzed using energy band theory. The results showed that the stress in (100) crystal plane had a great influence on the β of the vertical NPN and vertical PNP, and it had been verified by experiments.