The phylogenetic trees of the insect chemosensory proteins (CSPs) gene from 59 sequences of CSPs in 23 species under 7 orders published in GeneBank were generated by MEGA 5.0. Complete comparisons of CSPs sequences were used to determine the rates of synonymous(Ks) and nonsynonymous(Kn) codon substitutions and the ratio of Kn/Ks was calculated to estimate of the selection pressure on CSPs genes in insects.The Kn/Ks ratio was far less than 1,suggesting that CSPs may be evolving under negative selection.By the site-specific model in PAML 4.4, 6 amino acid sites undergoing positive selection were detected,5 of them were in the important function regions.