Objective To analyze the diagnostic value of diffusion weighted imaging (DWI) to differentiate the benign and malignant breast lesions, and optimize the b-value at 3.0T-MR. Methods MRI-DWI examination with different b values of 0, 400, 700, 850 and 1000 s/mm2 were applied to fifty-five cases of breast lesions which proved by biopsy or surgical pathology. Image quality score and apparent diffusion coefficient(ADC) values were compared among benign lesions, malignant lesions, normal glandular tissue and glandular tissue around the lesions using different b values. Results The difference of the image quality score was statistically significant(p<0.01) among the b-value 400, 700, 850 s/mm2 , but not between 850 and 1000 s/mm2(p>0.05). ADC values showed significant difference between breast benign lesions and malignant lesions, and among the glandular tissues around the lesions in different b value (P<0.01), but ADC values demonstrated no difference in the normal glandular tissue far away from the lesions (P>0.05). The diagnostic sensitivity, specificity, positive predictive value, negative predictive value and accuracy were higher than others when ADC was 1.24×10-3mm2/s following b value 0, 850s/mm2. Conclusion The best b-value may be 0,850s/ mm2 in breast DWI at 3.0T. ADC value will contribute to distinguishing benign and malignant breast lesions. The ADC value of the glandular tissue around lesion may be very important in differentiating benign and malignant breast lesions.