In this invention, three genes encoding short chain neurotoxin are obtained by sea snake--Lapemis hardwickii venom gland cDNA library construction and DNA sequencing, named sn12, sn36, and sn160, respectively. The three genes are modified and amplified by PCR method, then cloned into expression vector PETTRX. The three neurotoxin genes are all highly expressed in soluble fusion protein in E. coli stain BL21-DE3 which is used as a expression host when induced with IPTG. Studies on the analgesic effects of the three recombinant short chain neurotoxins showed that three proteins, SN12, SN36 and SN160 all can significantly increase the pain threshold value of mouse.