Abstract: Population dynamics and damage of green leaf bug，Lygus lucorum Mayr，on transgenic Bt cotton are studied in this paper．The results show that the bug num ber on GK-12 is not significantly different from that on its parent，but its degree of leaves damaged by the second generation of green leaf bug is much higher．There are no differences between SGK32 1 and its parent，when the number of green lea f bug and the degree of damaged leaves are compared．The damage index of total leaves on GK-12 is 1．27 times higher than that on SGK32 1．Thus，the damage of green leaf bug to transgenic Bt cotton，GK-12，is upward，while the population and damage on SGK32 1 are controlled in some extent．