Power VDMOS was widely used in various secondary power supply systems in aerospace field.However，the mechanical damage of chip existed in bonding process.Taking power VDMOS devices as the research object，it was clear that bonding failure was the damage caused by different degrees of mechanical action，the main factors of mechanical damage are chip structure，bonding material and bonding parameters.The results show that the damage degree can be divided into polysilicon damage，crack and crater from light to severe.The Al layer cushioned，and its thickness increases from 4 μm to 6 μm，which can reduce the damage degree.Microstructure analysis and simulation show that the damage occurs at both ends of the bonding point，the stress distribution of the bonding interface can be changed by adjusting the downward movement and amplitude.Reducing the bonding pressure and ultrasonic power can avoid bonding damage caused by stress concentration.