Objective To investigate the 3.0T high-resolution MRI before rectal cancer's preoperative staging of fine (TN staging, circumferential margin) to evaluate the accuracy, which would provide an accurate imaging basis for individualized treatment of rectal cancer. Methods A retrospective analysis of 109 cases was confirmed by the biopsy of patients with rectal cancer. The assessment of tumor size and nearby structures was made to analyze the T and N stage, CRM circumferential margin on MRI data, and postoperative pathologic results. Results MRI for mesorectum and mesorectal fascia clearly displayed peritoneal assessment of T staging, and MRI correctly staged 102 cases, among the 109 patients. The total accuracy was 93.58% (102/109). 3 cases were at low stages, and 4 patients were at high stages. For consistency test results of T MRI and pathological staging, Kappa value=0.873 and P=0.000, which suggests that the two diagnostic methods have a high consistency. MRI identified 92 cases at the correct stage, N stage, with an overall accuracy of 84.40% (92/109), as well as 11 cases at a high stage, and 6 cases at a low stage. 10 cases were involved in assessment of the CRM and MRI assessment of CRM involvement, while 99 cases were not involved. Consistency of DFS was 94.50% (103/109). Conclusion High-resolution MRI can clearly show mesorectum and mesorectal fascia structure before rectal cancer preoperative staging showed a good accuracy. MRI can provide accurate imaging basis for individualized treatment of rectal cancer.