The invention discloses a preparation method of N-doped DLC film capable of serving as a surface coating of a sliding element. The method is characterized by comprising the following steps that 1, a Si substrate which is strictly cleaned with acetone, ethyl alcohol, deionized water and the like is placed on a sample base frame; 2, nitrogen serves as gas for build-up of luminance to bombard target materials, and the purpose of removing surface impurities and activating the target materials is achieved; and 3, nitrogen also serves as reaction gas, namely a doping source, and doping of the DLC film is achieved through a reaction. According to the preparation method of the N-doped DLC film capable of serving as the surface coating of the sliding element, nitrogen serves as the gas for build-up of luminance and reaction simultaneously, fewer technological parameters are changed, and the N-doped DLC film which can serve as the surface coating of the sliding element and has a low friction coefficient can be prepared according to practical requirements.