Objective To explore the value of the plain scan and triple-phase contrastenhanced scans in the diagnosis of lung cancer. Methods A total of 52 patients with lung cancer admitted to our hospital from September 2016 to March 2018 were selected. The imaging features of lung cancer in the 256-slice flat-scan and triple-phase contrastenhanced scans were summarized, and the detection rate and diagnostic accuracy of the 256-slice flat-scan and triple-phase contrast-enhanced scans were calculated based on the pathological examination results. Results The total detection rate and diagnostic accuracy of the 256-slice extreme CT non-enhanced scanning for lung cancer were 92.30% and 88.46% respectively, the total detection rate and diagnostic accuracy of the 256-slice extreme triple-phase contrast-enhanced scans for lung cancer were 100% and 96.15% respectively, and the total detection rate of the 256-slice extreme triple-phase contrastenhanced scans for lung cancer was significantly higher than that of the 256-slice extreme CT non-enhanced scanning (100% vs 92.30%) (P<0.05). There was no significant difference in the overall diagnostic accuracy between the triple-phase contrast-enhanced scans and the CT non-enhanced scanning (P>0.05). CT scan images showed lesions: 23 cases of left lung, right lung 29 cases, CT scan shows most of the lesions was soft tissue density, the boundary is clear, tracheal bronchus cavity lesions images show the wide base with the trachea and into cavity, 5 cases of mediastinal large blood vessels of the lesions and adjacent structures boundary fuzzy, 4 cases of mediastinal lymph node enlargement. In triple-phase contrast-enhanced scans, most of the patients had obvious enhancement in arterial phase, and continuous enhancement in portal phase with the highest CT value, 16 patients showed heterogeneous enhancement, 5 patients showed "circular" enhancement, and mild and moderate enhancement in the balanced phase. Conclusion Both the nonenhanced scan and the triple-phase contrast-enhanced scans of the 256-slice rapid CT can effectively diagnose lung cancer, and display the image change characteristics of the lesions directly, and guide the clinical formulation of relevant treatment plans.