The invention is an on-monocrystalline silicon rare-earth nano-film self-composing preparing method, firstly preprocessing monocrystalline silicon slice, then dipping it in prepared rare-earth modifier, placing for 8 hours, take it out and wash by deionized water, airing it at room temperature and then placing in an oven, preserving heat at 120 deg.C for 1 hour, and obtaining the rare-earth self-composing film; where, the components of the rare-earth modifier in weight percent: rare-earth compound 3.5%-7%, alcohol 65%-85%, ethylene diamine tetra acetic acid 1%-4%, ammonium chloride 2%-5%, urea 10%-25%, and thick HCl 0.5%-1.5%. It has simple process, low cost, no environmental pollution, uniformly distributed rare-earth nano film, compact film formation, and obvious frication reducing action. Besides, the self-composing film has good wearability.