Abstract: The paper aims to investigate the effects of paclobutrazol on the growth of tobacco seedlings and rearing of Myzus persicae and Aphidius gifuensis, to improve the reproductive efficiency of A. gifuensis. In this experiment, using tobacco as the host of M. persicae to rearing A. gifuensis, three different concentrations of paclobutrazol were used to treat tobacco seedlings, and the different treatments were compared with the control. The growth of main stem height and maximum leaf area of tobacco seedlings, reproductive numbers of M. persicae and A. gifuensis were determined after different treatments with paclobutrazol. The results showed that, paclobutrazol treatment could significantly inhibit the growth of main stem of tobacco seedlings, the best results was the treatment of 400 times. The growth of leaf area of tobacco seedlings was also significantly inhibited, the effects of 400 times and 200 times were similar. There was no significant difference in the reproductive numbers of M. persicae and A. gifuensis among all treatments. More than 400 M. persicae could be reached on each tobacco seedling, reproductive A. gifuensis could also reach more than 200. All could achieve ideal reproductive effect. Paclobutrazol can significantly inhibit the growth of main stem and leaf area of tobacco seedlings, it is beneficial to the lodging resistance of the tobacco seedlings and reducing humidity between tobacco seedlings, and can improve the rearing effect of M. persicae and A. gifuensis. It has good popularization and application value in rearing A. gifuensis on a large scale.