Objective To investigate diagnosis value of differentiating central lung cancer from obstructive atelectasis by peneumonia at 3.0T MR. Methods Eighty-five cases diagnosed to be central lung cancer with obstructive atelectasis by clinic and pathology underwent 3.0T MRI scan. Scan sequences were as followed, T1WI, T2WI and DWI(b=0,400,1000s/mm2). ADC and SI(signal intensity) of central lung cancer and collapse lung tissues were measured and compared. The differentiation ability of T1WI, T2WI and DWI were compared. Results twelve cases could be distinguished on T1WI images, fifty-four on T2WI, sixty-five on DWI, seventy-three on T2WI and DWI. The differentiation ability of T2WI and DWI was superior to that of T1WI. The mean ADC value of central lung cancer(1.18±0.43)×10-3s/mm2 was significantly lower than that of collapse lung tissues(2.28±0.57)×10-3s/mm2(P<0.05). The mean signal intensity of central lung cancer was higher than that of obstructive atelectasis and pneumonia on DWI images(P<0.05). Conclusion 3.0T MRI can be used to differentiate central lung cancer from obstructive lobar collapse. DWI is an effective complement of T2WI.