Objective To investigate the value of the magnetic resonance imaging (MRI) with intrarectal water-bag in the preoperative staging of rectal cancer. Methods 36 rectal cancer patients proven by colonoscopy and pathology were inserted intrarectal waterbags into before MRI examination, by the comparison of preoperative MRI clinical stage (tumor T staging, lymph node metastasis N stage and circumferential resection margin involvement) and postoperative pathological results, the application value of MRI examination with intrarectal water-bag in resection of rectal cancer staging can be decided. Results There was an accurate correlation between pathologic and MRI examination with intrarectal water-bag in rectal cancer T stage and circumferential resection margin involvement (kappa value was 0.751, 0.769; P<0.01). The total accuracy rate of tumor T stage was 95%, the circumferential resection margin involvement in assessing the accuracy rate was 91.7%. The correlation between pathologic and MRI in node staging was generic (kappa=0.613; P<0.01), and the lymph node metastasis N staging accuracy rate was 80.6%. Conclusion MRI examination with intrarectal water-bag in tumor T staging diagnosis had great value, and it can accurately predict the circumferential resection margin involvement, and the lymph node metastasis and N staging can only make a general prediction.