Objective: To investigate the differential diagnosis effect of diffusion weighted magnetic resonance imaging (DW-MRI) scanning in patients with lung cancer. Methods: Prospective selection of 68 cases of lung nodules patients confirmed by conventional CT examination from May 2015 to February 2018 as the research objects, the patients were given conventional MRI and DWI before the surgery or needle biopsy, the results of pathology was the gold standard for diagnostic, then tested the lesion-to-spinal cord ratio (LSR) in different diffusion sensitivity coefficient (b value) of benign pulmonary nodules and malignant lung nodules, and analyzed the diagnosis value of LSR in differential diagnosis. Results: The 68 patients with pulmonary nodules underwent surgery or biopsy pathology showed that there were 38 patients with malignant pulmonary nodules (the malignant group) and 30 patients with benign pulmonary nodules (the benign group). The LSR value of malignant group when the b value was 400 s/mm² and 600 s/mm² were significantly higher than that of benign group (P<0.05). Compared with the pathological results, the sensitivity, specificity and accuracy of b value at 400 s/mm² were 63.16%, 73.33% and 67.65%, respectively. When the b value was 600 s/mm², the sensitivity, specificity and accuracy were 71.05%, 66.67% and 69.12%, respectively. According to the receive operating characteristic (ROC) curve, when the b value was 400 s/mm², the LSR value was 67.86% as the optimal critical value, the area under the curve was 0.691, and when the b value was 600 s/mm², the LSR value was 56.58% as the optimal critical value, and the area under the curve was 0.711. Conclusion: The calculation of LSR by DW-MRI had a certain clinical value in the diagnosis of malignant pulmonary nodules.