Objective To investigate the diagnosis efficiency of decline rate of signal intensity and apparent diffusion coefficient(ADC) with different b values for differentiating breast non-mass invasive ductal carcinoma(IDC) and ductal carcinoma in situ(DCIS) on diffusion-weighted 3.0T magnetic resonance imaging. Methods Collecting 78 cases of non-mass IDC and 32 cases of DCIS from June 2014 to December 2016 in Dongguan People's Hospital. All patients underwent 3.0T magnetic resonance imaging scan before operation, three b values (0,500,800s/mm2 ) were used. The signal intensity with different b value and ADC values with b value(800 s/mm2 )of breast cancers were measured respectively. The signal intensity decline rate(SIDR) was calculated. SIDR=(signal intensity of lesions with low b value- signal intensity of lesions with high b value)/ signal intensity of lesions with low b value. The independent sample t-test was employed for statistical analyses. Results (1) Non significant differences were observed in signal intensity between breast non-mass IDC and DCIS with b values of 0,500,800s/mm2 (P>0.05); (2) Non significant differences were observed in SIDR between breast non-mass IDC and DCIS with b values of 0-500,500-800s/mm2 (P>0.05); (3) Significant difference was observed in ADC value between breast non-mass IDC and DCIS with b values of 800s/ mm2 (P<0.05). Conclusion The signal intensity and decline rate with different b values may be not used for differentiating breast non-mass IDC and DCIS now; ADC value has some reference value with b value of 800s/mm2 .