Abstract: The population dynamics of cotton bollworm（Helicoverpa armigera Hübner）in transgenic cotton，SGK321，GK12 and 33B were studied.It showed that the damage rates of leaves，squares and bolls in transgenic cotton SGK321，GK12 and 33B fields were lower than those in non-transgenic cotton fields.There were much less larvae in the transgenic cotton fields during the second and third generations of H.armigera.Although the number of the fourth generation larvae in transgenic cotton fields was more than that of the third generation，it was still less than that in the non-transgenic cotton fields.There were no significant differences among transgenic Cry1Ac & CpTI cotton（SGK321），transgenic Cry1Ac & Abcotton（GK12）and transgenic Cry1Ac（33B）cotton，when the numbers of larvae and the damage rates of leaves，squares and bolls were compared during the second，third and fourth generations of H.armigera.It indicates that the resistance of SGK321，GK12 and 33B to cotton bollworm does not differ in the fields.