Two pairs of primers were designed according to the Nsp2 gene sequences of PRRSV TJ strain (EU860248). The hypervariable fragment of 1 004 bp of Nsp2 was amplified by RTPCR with primer pair ns–U and ns–L from TJ strain passaged on Marc-145. PCR products were cloned to pMD18T, and sequenced. Comparison among the hypervariable region showed that a 360 bp (encoding 120 amino acids)deletion in Nsp2 of PRRSV TJ strain was appeared in passage 18 and the deletion existed through passage 122. Full length Nsp2 gene was amplified with primer pair Nsp2–U and Nsp2–L from the 3rd generation(F3)virus and the 92nd generation(TJMF92)virus which is virulence attenuated to analyze the second structure of Nsp2 protein，the results showed the deletion of 120 amino acids caused space structure changes and it was speculated the deletion was related to the attenuated virulence and pathogenicity of PRRSV TJMF92.