Abstract: Failure mechanism and influence factors of Surface Mount Technology (SMT) of aerospace electronic products were analyzed reliability, and its elastic-plastic stress law and lifetime were researched under thermal cycling load, which was basis for exploring of thermal fatigue life under influence of clearance between component and welding plate, solder volume and external profile. This paper reveals the corresponding relationship among the shape of solder joint, stress strain and fatigue lifetime, with the intention to explore a solder joint share with relatively ideal mechanical property and thermal cycling life, and to provide theoretical basis for reasonable design of the size of solder pad on PCB, control of the quality of solder joints from the perspective of performance of joint in the actual process of soldering process.