Objective To investigate and compare the clinical value in CT and MRI in the preoperative diagnosis of lymph node metastasis in colorectal cancer. Methods From July 2011 to February 2015, Selected 78 cases of colorectal cancer patients in our hospital for treatment of oncology, preoperative CT and MRI were performed before oearation, observed the signs characteristics of CT and MRI. Results 78 patients after surgical pathology was confirmed 60 patients of lymph node metastasis (malignant lymph node group), 18 patients without lymph node metastasis (benign lymph node group), the lymph node metastasis rate was 76.9%. The CT diagnosis of lymph node size, short length by the ratio of the number of lymph nodes in the malignant lymph node group were significantly higher than benign group (P<0.05). MRI showed 42 patients were serosal infiltration, intravenous surrounding levy were 54 patients and 50 patients were intestinal fat mixed signals; and benign lymph node group were respectively 6 patients, 1 patient and 0 patient, the differences were statistically significant compared between the two groups (P<0.05). And pathological determination contrast, CT diagnosis of colorectal cancer lymph node metastasis of sensitivity and specificity were 100% and 94.4%, MRI diagnostic sensitivity and specificity were all 100.0%. Conclusion CT and MRI findings in the size of lymph nodes, short diameter ratio, the number of lymph nodes, serosa infiltration, intravenous surrounding syndrome, intestinal fat mixed signal levy week are all available Tip colorectal cancer lymph node metastasis, and the diagnostic specificity and sensitivity all were relatively well.