It is important and necessary to evaluate the extent of gene flow from transgenic cotton to weedy relatives such as weeds.But the premise is to understand the species and occurrence of weeds in the transgenic cotton fields.The species and harm of weeds in three types of transgenic cotton, non-transgenic cotton and blank control fields in the plant breeding base of Hainan were surveyed to explore the occurrence of weeds in different cotton fields.The results showed that there were 23 weed species of 15 families in transgenic Bt/CPTI cotton fields with the dominant weeds crowfootgrass, crabgrass, goosegrass with the relative abundance (RA) of 35.27, 29.81 and 26.53 respectively.