Effects of elevated CO₂ (750 μl/L) on the size, enzyme activity of Bemisia tabaci biotype B fed on two types of transgenic Bt cotton (GK-12) and nontransgenic cotton (S3) were conducted for three successive generations. The host selection behavior and oviposition in the third generation of B. tabaci biotype B were also investigated in Open-top chambers (OTC). The results showed that the sizes of egg, pupa, adult of both sex were not influenced by CO₂ level and cotton variety for the B. tabaci in the second and third generations. However, the length of pupa, both sex adult and the unfolded wing of female were significantly reduced in the first generation of B. tabaci grown under the elevated CO₂. Compared with that on ambient level of CO₂, the length of pupa, the length of adult female, and the unfolded wing of adult female B. tabaci fed on nontransgenic cotton (S3) grown in elevated CO₂ were reduced 2.81%, 2.95% and 0.94%, respectively. Similarly, the the unfolded wing of female and the length of adult male were reduced 2.08% and 2.58% for the the B. tabaci fed on GK-12 grown in elevated CO₂ compared with that on ambient level of CO₂.Furthermore, several important enzyme activities were analyzed in detailed. The Glutathione Stransferase (GSTs) activity was increased by 45.73% when B. tabaci was fed on GK-12 grown in elevated CO₂ in the third generation and the Acetylcholinesterase (AchE) activity was increased by 27.68% when B. tabaci was fed on S3 grown under elevated CO₂ in first generation. However, the GSTs activity was reduced by 35.12% when the B. tabaci wasfed on GK-12 grown in ambient CO₂ in first generation whereas the AchE was elevated by 30.28%. The activity of Carboxylic Esterhydrolase (CarE) was not significantly difference in the B. tabaci fed on the four treated cotton above. Furthermore, ANOVA analyses of CO₂, cotton variety and their interactions on above three enzymes suggested that the three enzymes affected by the level CO₂, GSTs activity was only affected by the cotton variety, AchE activity was affected significantly in generations,CO₂ ×generation interactions, and CO₂×variety×generation interactions. The CarE activity among three generations was not affected by the three factors. More adult numbers of B. tabaci were observed for preference to cottons grown in elevated CO₂ than in ambient CO₂.The numbers of B. tabai that fed on cottons grown in ambient CO₂ which preferred to cottons grown in elevated CO₂ were increased 9.175%, 19.89%, 27.93% compared with that fed on S3 grown in elevated CO₂, and GK-12 and S3 grown in ambient CO₂. Furthermore, the numbers of B. tabai that fed on cottons grown in elevated CO₂ which preferred to cottons grown in elevated CO₂ were increased 12.56%, 21.05%, 28.73% compared with that fed on S3 grown in elevated CO₂, and GK-12 and S3 grown in ambient CO_2. The number of eggs laid after 72 h that the B. tabaci fed on both GK-12 and S3 grown in elevated CO₂ were increased 24.55% and 19.03% respectively compared to that grown in ambient CO₂. Moreover, the egg numbers of B. tabaci that fed on KG-12 cotton grown in elevated CO₂ in F3 generation were increased 26.93% compared to that in ambient CO₂. The difference between these two treatments was highly significant. Our data indicated that the size, enzyme activity and host selection behaviorof B. tabaci biotype B can be changed under elevated CO₂ in the future.