Abstract: 【Objective】The study investigated the changes in major enzyme activities in different developmental stages of Bactrocera tau（Walker） fed on Siraitia grosvenorii（Swingle） C. Jeffery after host transfer, aiming to elucidate the host adaptation of B. tau from physiological and biochemical mechanism, and therefore provide a theoretical basis for its effective control. 【Method】The B. tau population collected from a S. grosvenorii orchard and fed with S. grosvenorii indoors for 2 years was transferred to four different host plants: pumpkin, loofah, cucumber, and S. grosvenorii. Then measured the activities of antioxidant enzymes superoxide dismutase（SOD）, peroxidase（POD）, catalase（CAT）, detoxifying enzymes glutathione S-transferase（GST）, carboxylesterase（CarE）, digestive enzymes pepsin, α-amylase, lipase（LPS）, and hydrolytic enzyme trehalase（THL） in 5-day-old larvae, 2-day-old pupae and 7-day-old adults. 【Result】The SOD activity of B. tau feeding on different hosts was significantly higher in the adult stage than in other developmental stages across all host plants（P＜0.05, the same below）. The CAT activity was significantly higher in the larval and adult stage feeding on S. grosvenorii than those feeding on other hosts. However, the CAT activity in the adult stage of B. tau feeding on different hosts was lower（except that the CAT activity in adults feeding on pumpkin was slightly higher than that in pupae） or significantly lower than those in other developmental stages. Similarly, B. tau feeding on S. grosvenorii showed higher or significantly higher GST activity at the same stage compared to those feeding on other hosts, while B. tau adults feeding on all host plants exhibi-ted significantly lower GST activity compared to other stages. The CarE activity in larval and pupal stages feeding on S. grosvenorii was higher or significantly higher than those on other hosts.The α-amylase activity of B. tau feeding on S. grosvenorii was higher or significantly higher than those on other hosts at the same stage. The LPS activity in larvae of B. tau feeding on pumpkin was higher than those feeding on other hosts and those in other stages. The THL activity of B. tau feeding on different hosts in the adult stage differed significantly, THL activity of B. tau feeding on pumpkin was significantly higher than those feeding on other hosts, THL activity of B. tau feeding on S. grosvenorii was significantly lower than those feeding on other hosts. 【Conclusion】B. tau possesses higher adaptability to S. grosvenorii, suggesting that S. grosvenorii is a more suitable host plant for the growth and development of B. tau compared with pumpkin, loofah and cucumber.