The invention discloses a lubricant for drilling fluid and belongs to the technical field of chemical agents for petroleum drilling engineering. The lubricant for the drilling fluid contains the following ingredients in parts by weight: 35-90 parts of vegetable oil, 10-25 parts of synthesized ester type oily agent, 9-21 parts of emulsifier, 3-8 parts of extreme-pressure antiwear agent, 6-18 parts of organic molybdenum compound, 10-12 parts of nano metal powder, 7-15 parts of dispersant, 5-9 parts of graphite powder, 3-8 parts of antifoamer, 4-7 parts of surfactant and 4-8 parts of antioxidant. According to the lubricant for the drilling fluid, disclosed by the invention, the vegetable oil serves as a main raw material, and other additives are added as adjuvants, so that the lubricating property of the drilling fluid can be remarkably improved after the lubricant is added into the drilling fluid; and meanwhile, the lubricant has high-temperature and high-pressure resisting characteristics and antiwear and antifriction properties and is free of a mineral oil ingredient, and the additives are also free of sulfur and phosphorus, so that the lubricant is environment-friendly.