Abstract: Objective: to analyze the MRI features of the mesentery lymph nodes of rectal carcinoma with high resolution T2 weighted imaging (T2WI), and to investigate the basis of using MRI to diagnose the lymph node metastasis of rectal cancer, so as to improve the preoperative N staging of rectal cancer. Methods: A retrospectiveanalysis of 62 cases of rectal carcinoma patients with MRI imaging in our hospital in April 2016~2017 year in March from data, respectively in the lymph node short diameter is greater than or equal to 3 mm and over 5 mm for reference, combined with the internal signal (divided into mixed signal and signal edge (uniform), divided into smooth edge and rough edge), the mesorectal fascia fat in lymph nodes were N staging, imaging diagnosis and pathological diagnosis Results, statistical analysis of MRI in the diagnosis of colorectal cancer preoperative N staging accuracy, sensitivity, specificity, positive predictive value and negative predictive value. Results: 62 patients only with lymph node positive index was greater than 5 mm, the diagnostic accuracy was 77.42%, sensitivity was 62.50%, specificity 86.84%, positive predictive value was 75%, the negative predictive value was 78.57%; the lymph node is greater than or equal to 3 mm as a positive index, the diagnostic accuracy was 75.80%, sensitivity 87.50%, specificity 68%, positive predictive value was 63.60%, the negative predictive value was 89.66%; the sensitivity is higher than that of the former, the difference was statistically significant (<i<P</i<<0.05), no significant differences in the remaining diagnostic efficiency (<i<P</i<<0.05). The combination of internal signal characteristics and the edge of the situation, 5 mm group, the accuracy was 83.87% more than the lymph node, the sensitivity was 62.50%, specificity 97.37%, positive predictive value was 93.75%, the negative predictive value was 83.43%; the 3 group mm diagnostic accuracy was 90.32% more than the lymph node, the sensitivity was 83.33%, specificity was 94.74%., the positive predictive value was 90.91%, the negative predictive value was 90%;the diagnostic efficiency was higher than the simple lymph node size for positive index improved, especially in lymph nodes more than 3 group mm diagnostic performance better, accuracy, specificity, positive predictive value of elevated significantly, the difference was statistically significant (<i<P</i<<0.05). Conclusion: only by the size of lymph node metastasis as standard, 3 mm, 5 mm with high sensitivity, but the specificity is low; the combined signal and the edge of lymph nodes, can significantly improve the diagnostic efficiency, and 3 mm more obvious.Therefore, in the determination of lymph node metastasis, a comprehensive analysis should be performed based on the size of the lymph nodes, combined with signal and marginal conditions.