Objective Overall tumor assessment such as histogram analysis was a common means to obtain tumor heterogeneity information that may affect the treatment response. The purpose of this study was to evaluate the role of functional magnetic resonance imaging MRI in analyzing tumor heterogeneity in evaluating the efficacy of radiotherapy and chemotherapy CRT for rectal cancer. Methods From January 2020 to November 2021 60 patients with locally advanced rectal cancer LARC who underwent MRI examination before CRT in our hospital were selected as the research subjects. The apparent diffusion coefficient ADC intra-voxel incoherent motion Dslow Dfast and F and stretch index model DDC and α were obtained from the histogram of the whole tumor. Histogram indexes and prognostic factors before CRT were compared between patients with complete pathological remission pCR and those without pCR. The receiver operating characteristic curve ROC curve was constructed to evaluate the diagnostic performance of these parameters. Results After CRT treatment 13 patients 21. 7% were classified as pCR group while the other 47 patients were classified as non-pCR group 78. 3% . Compared with the pCR group the non-pCR group had significant differences in tumor volume TRG and pT stages P < 0. 05 . The mean standard deviation and the 10th 25th 50th 75th 90th and 95th percentile of ADC in pCR group were significantly lower than those in non-pCR group P<0. 05 . The mean skewness kurtosis and 25th 50th 75th 90th and 95th percentile of DDC in pCR group were lower than those in non-pCR group P<0. 05 . In ADC its average value AUC = 0. 890 P<0. 001 95%CI = 0. 806-0. 974 had the highest diagnostic performance. In DDC its average AUC = 0. 866 P<0. 001 95%CI = 0. 771-0. 960 has the highest AUC value. Average ADC combined with tumor volume had the highest diagnostic performance in predicting pCR with AUC of 0. 932 sensitivity of 100% and specificity of 81%. Conclusion The whole-tumor ADC mean combined with the tumor volume can effectively predict the response of LARC to CRT.