Objective：To explore the risk factors of pathological complete response（pCR）after neoadjuvant chemoradiotherapy in locally advanced rectal cancer based on clinical and magnetic resonance imaging（MRI）data. Methods：A retrospective analysis was conducted on 175 patients diagnosed with locally advanced rectal cancer through biopsy and clinical diagnosis from December 2014 to November 2022，who underwent total mesorectal excision（TME）after neoadjuvant chemoradiotherapy. These patients were randomly divided into a training set and a validation set in a 7∶3 ratio. The training set included 122 patients，with 30 in the pCR group and 92 in the non-pCR group；the remaining 53 patients served as the validation set（10 in the pCR group and 43 in the non-pCR group）. Clinical data，imaging examination and pathological data of patients before and after treatment were collected. Univariate and multivariate logistic regression analyses were used to evaluate the efficacy of neoadjuvant treatment in locally advanced rectal cancer. The diagnostic efficacy of predictive factors was evaluated by receiver operating characteristic（ROC）curve. The diagnostic efficacy of predictive factors was assessed using the receiver operating characteristic（ROC）curve，calculating the area under the curve（AUC），cutoff value，sensitivity，and specificity. Differences in AUC values were compared using the DeLong test. Results：Statistically significant differences were observed in the maximum tumor diameter before and after treatment，the depth of tumor infiltration before and after treatment，the CEA value after treatment，the number of lymph nodes around the tumor after treatment，extramural vascular invasion before and after treatment，imaging T and N stages after treatment，and the mesorectal fascia between the pCR and non-pCR groups. The univariate and multivariate logistic regression analysis identified extramural depth after treatment was an independent risk factor for evaluating the efficacy of neoadjuvant chemoradiotherapy. Extramural depth after treatment demonstrated good diagnostic efficacy in predicting the efficacy of neoadjuvant chemoradiotherapy in both the training and validation sets. The AUC values for the training and the validation sets were 0.783 and 0.765，respectively，with cutoff values of 0.555 and 0.627，sensitivity of 0.870 and 0.852，and the specificity of 0.733 and 0.773. There was no statistically difference after Hosmer - Lemeshow goodness of fit test. Conclusion：Evaluating the extramural depth is helpful to evaluate the pCR rate of locally advanced rectal cancer after neoadjuvant chemoradiotherapy in locally advanced rectal cancer，providing a convenient and non -invasive diagnostic tool for clinic practice and guiding individualized treatment.