Glutathione peroxidase, one of the most important components of anti-peroxidation system of the organism, plays an important role in the responses of microorganisms to the environmental stress. In this study, three oxidative stress reagents were performed to determine the stress effect on glutathion peroxidase of Isaria farinosa. Results indicated that the early treatment of oxidative stress under three kinds of conditions all made the GPX activity of bacterium cells decreased. In the later period of cultivation, the GPX activity of bacterium cells under H202 stress had quite small difference compared to the contrast. While it were greatly increased compared to the contrast under the methylene blue and nitrosodisulfonate stress. The Pf340 strain showed diverse biological behavior in response to different oxidative stress.