Abstract: SMLUB-E, an environmental-friendly drilling fluid lubricant, was synthesized from natural fatty acids and organic polyols because the existing drilling fluid lubricant was not sufficiently temperature-resistant, nor did it have sufficient environmental friendliness. An evaluation conducted indoors in laboratory conditions demonstrated that when 1.0% SMLUB-E was added to bentonite mud, the friction coefficient could be as low as 0.05 while maintaining a high strength of lubricating film. When 2.0% SMLUB-E was added to polysulfonate drilling fluid, the friction coeffi-cient decreased from 0.31 to 0.08 with lubricity better than that of 8.0% crude oil added. SMLUB-E has a temperature resistance of 160 ℃, which has no adverse effect on rheological property and fluid loss of drilling fluid. Further, SMLUB-E is easy to biodegrade, non-toxic and environmental-friendly. Field Applications of SMLUB-E has conducted on deep wells including Well TP238CH in Tahe Oilfield, the drilling fluids added SMLUB-E showed good lubrication and friction-reducing property, significantly reduced downhole friction, avoided complex situations such as WOB hang-off and sticking, etc.. The results showed that SMLUB-E has a good performance in temperature resistance and environmental friendliness, and could effectively solve the technical problem of large downhole friction in the drilling of deep & ultra-deep wells.