[Ob.jcctive] This study aimed to investigate the spatial-temporal dynamics of Bt toxic protein expression in insect-resistant transgenic cotton and its degradation in soil. [Meth~d] BtcrylAc toxic protein expression in roots, stems and leaves of trans- genic cotton Guoshen GK45 at different developmental stages and the annual aver- age content of BtCrylAc toxin protein in the topsoil, rhizosphere soil and following cotton-growing area were explored and analyzed by using enzyme linked immuno sorbed assay （ELISA）. [Result] The content of exogenous BtCrylAc toxin protein de- creased during the growth process of insect-resistant transgenic cotton; to be specif- ic, the content of BtCrylAc toxin protein in cotton stems and leaves decreased more slowly and always maintained a high level, while that in roots decreased rapidly and reached a minimum level to the following plant growth and development stage. BtCrylAc toxin protein was detected in topsoil of both non-transgenic and transgenic cotton-growing areas, and the content of BtCrylAc toxin protein increased in topsoil of following cotton-growing area, which was very low in rhizosphere soil. [Conclusion] Determination of BtcrylAc toxic protein provides scientific basis for the risk assess- ment of the cultivation of genetically modified crops and the safety evaluation of soil ecosystem.