Objective To investigate the features of MR DWI with different b values, changes of ADC value, correlation of ADC value with Ki-67 expression in early breast cancer. Methods 35 patients with early breast cancer underwent MR DWI scanning with different b values, including 500s/mm2 、800s/mm2 、1000s/mm2 .The ADC values of the tumor lesions were measured after scanning with different b values. The DWI signal features of the tumor lesions were analyzed. The differences of the ADC Values were statistically compared, and the correlations of ADC values of the lesions with Ki-67 expressions were statistically analyzed. Results All of the patients were early breast invasive ductal carcinoma. All of the tumor lesions showed obviously high signal in DWI. There were statistically significant differences(P<0.05) between the mean values of the group of b-value 500s/mm2 (group of b-500) with group of b-value 800s/mm2 (group of b-800), Group of b-500 with group of b-value 1000s/mm2 (group of b-1000),respectively. However, there was no statistically significant difference(P>0.05) between the group of b-800 and group of b-1000.The mean ADC values were 1.1416×10-3mm2 / s(group of b-500), 0.9258×10-3mm2 /s (group of b-800), 0.8668×10-3mm2 /s(group of b-1000),respectively. The correlations between the ADC values of the three different b-value groups and the Ki-67 expressions were not statistically different(P>0.05). Conclusion There are certain differences between the ADC values measured after DWI scanning with different b values in early breast cancer. It is more suitable to select b-value 800s/mm2 for DWI scanning in breast cancer. It is possible to diagnose early breast cancer when the ADC value is less than 0.9258×10-3mm2 /s.The ADC value of early breast cancer was not obviously correlative with Ki-67 expression.