Objective To investigate the application value of energy spectrum CT in the diagnosis and pathological typing of lung cancer. Methods 80 patients with suspected lung cancer treated in our hospital from January 2015 to June 2017 were selected as study subjects. They were examined by energy spectrum CT scan after admission, and according to histopathological findings, the effectiveness of energy spectrum CT in the diagnosis of lung cancer was evaluated. Patients with lung cancer were divided into squamous cell carcinoma group, adenocarcinoma group and small cell carcinoma group according to postoperative pathological findings. The spectral characteristic parameters and spectrum curves were compared among the three groups after plain scan and enhanced scan. Results With histopathological findings as the golden standard, the sensitivity, specificity, accuracy, positive predictive value and negative predictive value of energy spectrum CT in the diagnosis of lung cancer were 83.33%, 65.00%, 87.72% and 56.52% respectively. The calcium content and effective atomic coefficient of small cell carcinoma group were the highest, followed by squamous cell carcinoma group and they were the lowest in adenocarcinoma group. There were statistically significant differences between any two groups (P<0.05). For comparison of △Ct value among the three groups, only △Ct value in adenocarcinoma group was significantly higher than that in small cell carcinoma group (P<0.05). K and NIC slopes in the three groups ranking from high to low showed small cell carcinoma group > squamous cell carcinoma group > adenocarcinoma group, and there were statistically significant differences between any two groups (P<0.05). The sensitivity and specificity of slope K in differential diagnosis of squamous cell carcinoma and adenocarcinoma were 85% and 89% respectively, and the area under the curve was 0.92. Conclusion Energy spectrum CT can be used as an effective assistant method for the diagnosis of lung cancer and differential diagnosis of pathological type.