The invention discloses a preparation method of a resin material with medium refractive index and a lens thereof. The resin material is polymerized by four monomer components A, B, C and D; the component A is diisocyanate with napthene, the component B is an isocyanate compound with open chain methylene, the component C is a mercapto propionate compound, and the component D is a thioether compound. According to the resin material with refractive index, chemical monomers with special structure and good optical performance are selected, a suitable catalyst is added, and a corresponding lens forming technology is formulated to prepare an impact resistant resin lenses with strong toughness and refractive index of 1.56-1.57. The prepared lenses is subjected to surface stiffening and coating, and through a falling sphere test by fall free of a 16 g steel ball from the height of 1.27 m, the lens is unbroken by three consecutive tests, and can pass the United States FDA standards.