To investigate the clinical efficacy of Zengye Tongbian decoction in treating 90 cases of functional constipation by a randomized, double- blind, parallel- controlled trial. In treatment group, the total significant effective rate was 76.67%, and the total effective rate was 93.33%, which were significantly higher than that of control group (13.33% and 36.67% separately) (P<0.05). For Yin deficiency and dry intestine syndrome, the total significant effective rate in treatment group was 72.22%, and the total effective rate was 88.89% which were significantly higher than that of control group (13.33% and 30.00%) (P<0.05).