Abstract： Objective To explore the differential diagnosis value of DWI ADC for breast lumps,improve the diagnosis of breast cancer specificity.Methods 93 patients with 105 breast tumors were performed with routine MR series and DWI,and the ADC values were measured.Results Lesions ADC values:average ADC value 43 benign lesions in 37 cases was(1.37±0.36)×10-3 mm2/s,the different value between max and min was(0.63±0.19)×10 -3s/mm2.Average ADC value of 62 malignant lesions in 58 patients was(0.90±0.53) × 10 -3 mm2/s,the different value between max and min was(0.91±0.27)×10-3 mm2/s.By statistical analysis,both average ADC values and the max and the min ADC difference value were very significantly different(P＜0.01).Draw diagnosis benign and malignant lesions ROC curves,with ADC values 0.11×10 -3 mm2/s for critical value to judge benign and malignant standard,sensitivity was 67％,specificity was 72％.With 1.0×10- 3 mm2/s for critical value,specificity can raise to 84％,and sensitivity came to 60％.With the maximum and minimum ADC difference value 0.75 × 10-3s/mm2 for critical value,sensitivity was 67％,specificity was 68％.If with 0.80 for critical value,sensitivity was 53％ and specificity 82％.Conclusion The average ADC values of DWI were significant for the identification of benign and malignant lesions.