Objective:To explore the mechanism in patients with irritable bowel syndrome (IBS) of the Forty-seven IBS patients with the constipation predominant type were randomly divided into the treated group (n=24) and the control group (n=23). Another group of 22 healthy subjects was set up for healthy control.The treated group was treated with modified SNS, and the control group was treated with Cisapride, the therapeutic course for both groups was 8 weeks. The changes of symptom scoring and anorectal manometry (the anorectal resting pressure, anal tract systolic pressure, anal tract diastolic pressure, rectal threshold feeling, maximal tolerance volume of rectum, and rectum compliance) of these two groups were recorded respectively and compared with each other. Results: Compared with the healthy control group, the rectal threshold feeling, maximal tolerance volume of rectum and rectal compliance of the treated groups got reduced significantly before treatment (P＜0.05). After treatment, the symptom scoring, rectal threshold feeling and maximal tolerance volume of rectum were improved in both groups (P＜0.05), and the improvement of the treated group was more significant than that of the control group(P＜0.01). The total effective rate and recurrence rate of the treated group were superior to those of the control group significantly (P＜0.05,P＜0.01). Conclusion: SNS has good effect on IBS of the constipation predominant type.