Abstract: The impact of transgenic Bt cotton on non-target pest, natural enemies and economic insects along with impact factors were discussed in this article. Numerous studies indicated that the transgenic Bt cotton make the population of the secondary pests which are not susceptible to Bt protein in plant increase evidently or show aggravating trend，but there are no evidences proving that the transgenic Bt cotton have direct stimulative effect on the occurring of other pests in the cotton field. After the exotic Bt gene introduced into cotton genome, the changes of content of important cotton nutrition and form frame of cotton leaf maybe affect the number of cotton pests population directly. And transgenic Bt cotton field is more in favor of the occurring and harming of the secondary insects originally fed on other plant. The pests population number and Bt protein also affect the enemy number directly or indirectly. Now, many studies indicated that the transgenic Bt cotton have no evident impact to economic insects such as silkworm and bee etc.