Objective To analyze the clinical effect of CT (spiral, computed tomography) in the preoperative application and N staging in rectal cancer, and to evaluate the application value of SCT MRP (Multiplannar, reconstruction) in the measurement of the distance from the anus. Methods By colonoscopy and biopsy in 46 cases confirmed patients with rectal cancer underwent SCT examination, including 33 cases of rectal cancer, the status, the results were compared with the postoperative pathological findings, analysis of SCT for preoperative staging accuracy; and is beneficial to the SCT 3D imaging technology, digital rectal examination, colonoscopy and distance three methods of patients with lower margin to the anal margin were measured and compared with the actual distance is measured after operation, analysis of SCT measurement accuracy; and in 15 cases of patients with distance less than or equal to 6cm were determined to compare SCT with rectal examination accuracy. Results The accuracy of SCT T staging was 73.9%, and the accuracy rate of T staging of rectal cancer was 92.8%, the accuracy of N staging was 67.4%, the sensitivity was 91.3% and specificity was 69.6%. The results of Kappa test showed that the consistency of the medium was 0.479 and 0.569 respectively. The other SCT, digital rectal examination and colonoscopy methods of inspection accuracy was 84.8%, 48.5% and 36.4% respectively,and the difference was significant (P<0.005). In the 15 patients with low rectal cancer (the actual distance is less than or equal to 6cm),the accuracy of SCT and dre had no significant difference (P=0.245). Conclusion SCT has a high reliability of preoperative staging of rectal cancer, but the diagnosis accuracy of T2 and T1 is not high. In the middle and low rectal cancer patients, the three-dimensional imaging technology is very accurate,which can be promoted and applicated.