A recombinant expression plasmid was constructed by inserting the cDNA fragment encoding human sperm membrane protein (HSDⅡ) into pGEX vector. High level expression of the fusion protein was observed in the DH5α bacteria transformed with the recombinant pGEX vector in the absence of IPTG as well as after IPTG induction according to PAGE detection. A simple and valid method was recommended to minimize the basal level expression without IPTG induction: a plasmid pREP4 carrying LacⅠ gene was cotransformed with the recombinant expression plasmid into DH5α, and the basal level expression of the fusion protien was inhibited significantly while the presense of pREP4 did not affect overall expression following induction with IPTG.