Abstract：Objective：To observe the effect of modified Dahuang Mudan Decoction on intestinal flora and Th1/Th2 cytokines in patients after surgery for colorectal cancer (CRC) with damp- heat accumulation syndrome. Methods： A total of 96 cases of CRC patients with damp- heat syndrome were selected and divided into the observation group and the control group according to the random number table method， with 48 cases in each group. Both groups underwent laparoscopic surgery for CRC. After surgery， the control group was treated with routine chemotherapy and the observation group was additionally treated with modified Dahuang Mudan Decoction based on the treatment of the control group. Both groups were treated for 2 chemotherapy cycles， with 14 days being a chemotherapy cycle. Intestinal flora indexes， immune function indexes， Th1/Th2 cytokines levels， and the incidence of adverse reactions were compared between the two groups. Results： After treatment， the numbers of enterococcus faecalis， bifidobacterium， and lactobacillus in the two groups were decreased when compared with those before treatment (P＜0.05)，and the numbers of enterococcus faecalis，bifidobacterium，and lactobacillus in the observation group were higher than those in the control group (P＜0.05). The numbers of escherichia coli in the two groups were increased when compared with those before treatment (P＜0.05)，and the number of escherichia coli in the observation group was lower than that in the control group (P＜0.05). The levels of CD3+ and CD4+ and the values of CD4+/CD8+ in the two groups were decreased when compared with those before treatment (P＜0.05)，and the levels of CD3+ and CD4+ and the value of CD4+/CD8+ in the observation group were higher than those in the control group (P＜0.05). The levels of interleukin (IL)- 2 and interferon (INF-γ) in serum in the two groups were increased when compared with those before treatment (P＜0.05)， and the levels of IL- 2 and INF- γ in serum in the observation group were higher than those in the control group (P＜0.05). The levels of IL-10 and IL-6 in serum in the two groups were decreased when compared with those before treatment (P＜0.05)，and the levels of IL-10 and IL-6 in serum in the observation group were lower than those in the control group (P＜0.05). The incidence of adverse reactions was 10.42% in the observation group， lower than that of 27.08% in the control group (P＜0.05). Conclusion： Modified Dahuang Mudan Decoction for patients after surgery for CRC with damp-heat accumulation syndrome can improve the distribution of intestinal flora，promote the recovery of immune function，regulate the levels of Th1/Th2 cytokines，and reduce the incidence of adverse reactions.