Objective To investigate the diagnostic value of MRI combined with DWI in treating peritoneal metastatic carcinoma. Methods 45 cases with peritoneal metastatic carcinoma in our hospital from January 2014 to December were selected and analyzed by two radiologists with senior professional post. They were given MRI and MRI combined with DWI treatment in order to judge whether or not had peritoneal metastatic carcinoma. Diaphragm, douglas pouch, right paracolic sulci, left paracolic sulci, omentum and mesentery were emphatically observed. Compare the sensitivity, specificity and coincidence rate of MRI and MRI combined with DWI treatment. Results Sensitivity and specificity of MRI, MRI combined with DWI were 69.70% and 71.43%, 96.77% and 78.57%. Coincidence rate of MRI group (73.33%) was obviously lower than MRI combined with DWI group (91.11%), the difference was statistically significant (χ2 =4.865, P<0.05). Conclusion MRI combined with DWI in treating peritoneal metastatic carcinoma can improve diagnosis accuracy of peritoneal metastatic carcinoma, lower false positive rate and is worthy of wide application.