Silver tin oxide contact material is widely used in the contacts of electromagnetic relays. Its electrical contact characteristics and reliability theory under various load conditions have always been a research direction that relay manufacturing companies are very concerned about. In order to clarify the failure mechanism of silver tin oxide contact materials under different loads, this paper based on the designed electrical performance simulation experimental system of contact materials, observed the dynamic waveform characteristics of contact closing and breaking, and combined with the durability experiment to point surface topography scanning observation chart, starting from the perspective of arc and material transfer, based on the PSD model, the failure mechanism of the contact material under different loads was studied, and the degradation rules and characteristics of sensitive parameters during the experiment under different load conditions were verified.