Objective To investigate CT imaging changes before and after chemotherapy in 65 patients with lung cancer and to explore its application value in evaluating the efficacy of chemotherapy. Methods 65 patients with non-small cell lung cancer in the hospital were selected as the research objects. All were confirmed by fiberoptic bronchoscopy or puncture histopathology. Vinorelbine combined with cisplatin chemotherapy was chosen for treating lung squamous carcinoma while pemetrexed combined with cisplatin chemotherapy for adenocarcinoma and large cell carcinoma. The curative effect of chemotherapy was analyzed and the CT imaging changes were compared before and after chemotherapy. Results Among the 65 patients with lung cancer in this group, there were 13 cases with CR, 17 cases with PR, 15 cases with SD and 20 cases with PD. The total remission rate was 45.15%. The CT values at 60s and 25s before and after the treatment were higher than that at 0s (P<0.05). After chemotherapy, the corresponding CT density at 0s, 25s and 60s in the relief group was significantly lower than that of the non relief group and the difference was significant (P<0.05). Before chemotherapy, 37 cases of central lung cancer manifested as visible soft tissue density shadows in bronchus, the wall thickening, lumen irregular stenosis and 12 cases complicated with pulmonary atelectasis. There were soft tissue mass shadows in lungs of 28 cases with peripheral lung cancer, which were round or irregular, with rough edges. There was mediastinum and lymphadenectasis in 8 cases. After chemotherapy, with CT reexamination, the masses in patients with lung cancer in the relief group were shrinked, with unsharp boundaries. 9 cases were with pulmonary atelectasis opening. Conclusion Multi slice spiral CT dynamic scan can be used as an important imaging method for evaluating the efficacy of chemotherapy for lung cancer.