Abstract: Objection: Analysis and research on MRI subtraction technology combined with the clinical value of DWI in preoperative TN staging of rectal cancer can. Methods: Collected during 2010.8-2013.12 by surgery and pathology confirmed in our primary 53 patients with rectal cancer, The selected patients were confirmed by colonoscopy biopsy for 46 cases of patients with rectal cancer, 7 cases of suspicious. Including conventional MRI sequence TSE-T1 WI, T2 WI, diffusion imaging (DWI) can imaging and inversion recovery frequency saturation (SPIR) sequence. All patients were multiple enhanced scan, and ensure that there is a bearing insufflate long axis of the plane must be perpendicular to the masses, to subtract the same level images of before and after enhancement scanning. By two high venture experts asked to read, and preoperative TN staging. Pathological reference standard is a standard with Dukes staging.MRI subtraction technique in colorectal cancer using Kappa. test preoperative staging and pathologic results consistency difference, statistical processing using SPASS19.0. Results: 53 patients for colorectal cancer, MRI subtraction technique combining DWI for colorectal cancer detection rate of 100%, can correct the T staging in 49 cases, low stage 1 case, high stage (3 cases) , T staging accuracy was 92.5% (49/53). According to the preoperative MRI tips, surgical removal of lymph nodes 283, 53 patients with postoperative disease inspection in 36 cases with lymph node metastasis, 184 metastatic lymph nodes, DWI combined with conventional sequence can reliability evaluation of preoperative lymph node metastasis. Conclusion: MRI subtraction technique combining DWI convenient, quick, can in colorectal cancer diagnosis and preoperative TN staging accuracy is high, is worth popularization and application.