Objective: To study the relationship between intal anal sphincter function and length of remaining rectum after resecting rectal carcinoma. Methods: Preoperatively,21 patients were evaluated via patients’ clinical date,including anal resting pressure (resting pressure) assay.Six months postoperatively, repeated manometric studies and clinical evaluations were performed to assess the level of continence. The formula use for calculating postoperative resting pressure is as follows: postoperative resting pressure=0.42×preoperative resting pressure+1.56×length of remaining recturm+12.37 (R2=0.58; P＜0.01).Degree of continence was graded based on severity of the dysfunction and grade of the continence score. Results:It was demonstrated the patients with low postoperative resting pressures (＜4.0 Kpa) had incontinence, and those with high postoperative resting pressures (＞4.7 Kpa) were continent. There were significant correlations between length of the remaining rectum and ratio of the decrease in maximum resting pressure (postoperative/preoperative maximum resting pressure; r=0.62; P＜0.01). Conclusion:Continence of rectum is influenced by maximum resting pressure of function of the intal anal sphincter, length of remaining rectum is shorter, the more damage to the intal anal sphincter. It is able to foretell stool incontinence by using the postoperative resting pressure formula, and to determine the length of the remaining rectum.