When earthworms are exposed to pollutants, their antioxidant system will have responses immediately. Consequently earthworms are widely used to monitor various pollutants as sensitive bioindicator organisms. However, there are a large number of indices associated with the oxidative stress response. Finding out the key monitoring indices in the stress process becomes a practical demand of pollution monitoring and warning process. Factor analysis approach is a statistical method that uses a few factors to replace many original factors. This paper is aimed at analyzing and sorting factors related to Cd²⁺ on the earthworm Eisenia fetida under oxidative stress. Our experiment was divided into two groups: shortterm test and longterm test. The former one was for ten days, taking out an earthworm every day for analysis; The latter test lasted for 30 days, taking out an earthworm every ten days. The Cd²⁺ concentration was set at 0, 50, 100, 125, 250 and 500 mg·kg^-1. Postclitellum segments of earthworms were chosen to determine SOD, POD, GPX, GST, CAT, VE, MDA and AChE. The results showed that in the shortterm group, the main bioindicator associated with oxidative stress reaction was CAT at the exposure time of 1-3 days, MDA at 4-5 days, POD at 6-7 days, and GST and GPX at 8th day, CAT at days 9-10. With the longterm test, GPX was the main bioindicator associated with oxidative stress reaction.