The principle of baculovirus expression system is that substitute exogenous gene for polyhedrin (polh) gene, and the recombinant baculovirus lacks the ability to infect insect larvae by oral inoculation. In this study, we cloned the polh gene with immediate early gene 1 (ie1) promoter of Bombyx mori nucleopolyhedrovirus (BmNPV) into transposon pigA3GFP vector, transported it into BmN cells by lipofectamine and obtained the transgenic BmN cell line. The mRNA transcription of the polyhedrin gene was demonstrated by reverse transcription-polymerase chain reaction. Then the polh gene negative viruses (BmPAK6 and BmGFP), infected the transgenic BmN cells and Polyhedrin-like structures were observed in the infected cells. Subsequently, the viruses (vBmPAK6 and vBmGFP) from infected cells were used to orally inoculated the fifth instar larvae of B. mori, respectively. The results showed that B. mori larvae could be infected per os with the recombinant baculoviruses vBmPAK6 and vBmGFP, respectively. These results suggest that the products of polh gene expressed in the transgenic BmN cells could package the recombinant baculoviruses when the viruses infected the cells and raise the pathogenicity of the recombinant virus in orally infected B. mori larvae.