Three indices, i.e. severity, percentage of rolled leave and injure degree were used to evaluate the virulence of Thrips oryzeato both Bt gene transformed rice Kemingdao 2 and it's original parent Xiushui 11. The results indicated that Kemingdao 2 is much more susceptible to the rice thrips than Xiushui 11. There were no significant difference at thrips’ adult populations, while significant difference at eggs and nymphs population between Kemingdao 2 and Xiushui 11.It is indicated that a higher nymph population could cause more serious injure in Kemingdao 2.