To evaluate the efficacy and safety of TCM decoction Chang'an I Recipe in the treatment of IBS-D. A multicenter, randomized, double-blind, placebo-controlled clinical trial was designed. Patients were applied for central random number and were given corresponding treatment according to inclusion sequences.The treatment group was administered the Chang'an I Recipe, 150ml/bag, 3 times/day; while the control group was administered the placebo, 150ml/bag, 3 times/day. Both courses of treatment were 8 weeks.