To investigate the clinical effect of modified Wendan Decoction in treating chronic schizophrenia with phlegm dampness type. Methods:A total of 84 patients with chronic schizophrenia admitted in our hospital from December 2014 to December 2016 were randomly divided into observation group (n=42) and control group (n=42). The control group was treated with Olanzapine Tablets, while the observation group was treated with Jiawei Wendan Decoction on the basis of the control group. Two groups were treated for 6 weeks. The therapeutic effects of the two groups were compared before and after treatment. The PANSS score, LOTCA score, HAMA score, HAMD score, Hcy and SOD levels were observed before and after treatment. Results:The total efficiency of the observation group (90.48%) was higher than the control group (71.43%) (P<0.05); after treatment, PANSS scores decreased and LOTCA scores increased (observation group t=47.623,30.606, control group t=29.912, 16.134, P<0.05); after treatment, PANSS score of the observation group was lower than that of control group and LOTCA score was higher than the control group (t=16.252, 12.684, P<0.05); the HAMA score and HAMD score decreased in two groups after treatment (observation group t=37.449,35.239, control group t=25.738, 26.646, P<0.05); after treatment, HAMA score and HAMD score of observation group were lower than the control group (t=11.270, 8.867, P<0.05); the serum Hcy levels of the two groups after treatment decreased, and SOD level increased (the observation group t=15.991,24.989, control group t=7.283, 11.239, P<0.05); the serum Hcy levels after treatment in the observation group were lower than in the control group and the level of SOD was higher than that of control group (t=9.002, 14.957, P<0.05); the incidence of adverse reactions in the observation group (11.90%) was lower than that in the control group (33.33%) (P<0.05). Conclusion:The clinical effect of Jiawei Wendan Decoction in treating chronic schizophrenia with phlegm dampness type is significant, and it has important research value.