The invention discloses a light-weight, high-toughness and low-water-absorption-ratio ultra high molecular weight polyethylene (UHMWPE) / nylon 6 micro-foaming composite material and a preparation method thereof. The composite material is prepared from 97 to 99 weight percent of a polyamide composite material and 1 to 3 weight percent of a chemical foaming agent, wherein the polyamide composite material is prepared from the following components in parts by weight: 53 to 82 parts of PA6 (Polyamide 6), 6 to 12 parts of a compatilizer, 10 to 30 parts of UHMWPE, 3 to 5 parts of a modified inorganicnucleating agent, 0.2 to 0.4 part of an antioxidant, 0.5 to 1 part of a lubricant and 0 to 2 parts of other auxiliary agents. According to the light-weight, high-toughness and low-water-absorption-ratio ultra high molecular weight polyethylene / nylon 6 micro-foaming composite material, HDPE (High-density Polyethylene)-g-GMA (Glycidyl Methacrylate) is used as an interface bulking agent so that the interface binding force between the UHMWPE and the PA6 is enhanced, the impact strength of the PA6 is improved and the water absorption ratio of the PA6 is reduced; meanwhile, three-phase chain sections are mutually entwisted so that the melt strength of the PA6 is improved; the modified inorganic nucleating agent is subjected to chemical grafting modification through KH550 and GMA and the heterogeneous nucleation effect is remarkable; a dense bubble nucleation point is formed and the micro-foaming material with dense, fine and smooth bubble pores is obtained; the material has the characteristics of light weight, high impact strength, low water absorption ratio, high wear resistance and the like; foaming is realized through direct injection molding and a technology is simple; the material is widely applied to a lightweight technology of automobiles, household appliances, electronics and electrical appliances and the like.