The invention relates to a preparation method for nonlinear optical metal-organic boron polymer crystal material provided with equal chirality. The method adopts the steps that firstly, ligand H3L, namely tri-(4-para benzoic acid-2, 3, 5, 6-tetramethylbenzene) borane is synthesized, and then nonlinear optical metal-organic boron polymer crystal material with equal chirality is prepared, namely, ligand H3L and metal salt are mixed according to 1: 2, and dissolved by using N, N-dimethyl acetamide and methyl alcohol, the reaction liquid is positioned into a sample bottle for reaction, after the reaction is finished, the sample bottle is cooled to room temperature, the generated metal-organic polymeric material is taken out, and washed with ether for multiple times and air dried to obtain thematerial. The structural general formula is <M2L (OH) (MeOH)>.3H2O, wherein, metal M represents cobalt, manganese, nickel, copper, zinc or cadmium. The material produced through the invention has verygood second order nonlinear optical property, and compared with KDP, and the generation effect of second harmonics is 1.5 times higher.