Abstract: This article mainly explored the influence of thermal effects on the microstructure, tribological properties and rheological properties of complex lithium base grease and grease with Zinc dialkyl dithiophospahtes (ZDDP). After the grease samples were heated at a constant temperature of 120 ℃ and 150 ℃ for 24 hours, their appearance, infrared spectrum, boundary lubrication performances, elastohydrodynamic lubrication performances and rheological properties were tested. The research results revealed that the thermal effect of 120 ℃ had slight effect on the overall performance of lithium complex grease. However, the soap fibers of base grease and grease with ZDDP became looser and showed some breakdown, and the gelling network were also severely damaged after heated at 150 ℃. In addition, the structural strength and thixotropy of the grease also became worse. The thermal effect at higher temperature caused more serious damage to the microstructure of the greases, which resulted in significant changes of the properties.