The invention discloses a solid lubricant and its preparation method and application. The solid lubricant is prepared by mixing the following raw materials in parts by weight: 18-24 parts of dipentaerythritol, 28-32 parts of polytetramethylene glycol, and SG100 38~48 parts, 6~12 parts of thiourea. When preparing, add polytetramethylene glycol and SG100 into the mixing container, heat to 70-90°C, after the two melt into liquid, keep the temperature at 70-90°C, slowly add dipentaerythritol and thiourea under stirring condition, Stir for 1.5 to 2 hours to make it fully mixed and react, and cool to room temperature after the reaction to obtain a solid lubricant. The lubricant is in solid form, which is convenient for storage and transportation, has good lubricating performance, has a significant effect of reducing friction, can effectively improve the lubricating performance of drilling fluid, and has a low fluorescence level, does not affect geological logging, is non-toxic and harmless, and is environmentally friendly. The preparation method is simple, the conditions are mild, and the preparation cost is low.