To optimize the high b values (>200s/mm2) for intravoxel incoherent motion imaging of rectal cancer and to observe the effect of high b values variation on IVIM parameters. Three groups (A group with all 16 b values: 0,10,20,30,40,60,80,100,150,200,400,800,1000,1200,1500,2000, B group with 14 b values: 0,10,20,30,40,60,80,100,150,200,400,800,1000,1200 and C group with 12 b values: 0,10,20,30,40,60,80,100,150,200,400,800) were selected respectively for measurement by a radiologist. The average values of each measurement were used for statistical analysis. One-way analysis of variance (ANOVA) and post-hoc test were performed on the mean values of IVIM parameters in groups A, B, and C, with a significance level of P＜0.05. The p values of ANVOA results in ADC、D、D* values were less than 0.05, the differences were statistically significant. The p values of Bonferroni post-hoc test in D、D*、f values were not statistically significant differences in group A and B. With the number of high b values decrease, the values of ADC、D、D* values and standard error were increased, while of f values was not changed significantly. In our study, the reproducibility of the IVIM parameters caused by high b value variation was not significant. The value of selected b > 1500 need to be further studied.