Objective:To explore the pattern of lymph node metastasis in the lung lobes of stage Ⅱa non-small cell lung cancer (NSCLC) and the lymph node dissection method during complete video-assisted thoracoscopic lobectomy surgery (cVATS) .Methods:A total of 244 patients with NSCLC who underwent cVATS treatment at Nanjing Tongren Hospital Affiliated to Southeast University School of Medicine from January 2015 to November 2018 were selected. Patients admitted from January 2015 to April 2018 were defined as the training set ( n=183), and patients admitted from May 2018 to November 2018 were defined as the validation set ( n=61). The training set was used to build the model, and the validation set was used to evaluate the performance of the model. In the training set, patients were divided into systematic meditational lymphadenectomy (SML) group ( n=93) and lobe-specific systematic node dissection (LSND) group ( n=90) based on lymph node dissection methods. The lymph node metastasis rate of patients in the training set was calculated, and the clinical data of patients with ( n=55) and without ( n=128) lymph node metastasis were compared. Multivariate logistic regression was used to analyze the influencing factors of lymph node metastasis, and a nomogram prediction model was constructed based on the results of the multivariate analysis, and the model was validated. Clinical data, perioperative clinical indicators, overall survival (OS), and incidence of postoperative complications were compared between the SML group and LSND group in the training set. Results:In the training set, the lymph node metastasis rate of 183 patients with NSCLC was 30.05% (55/183), with a total of 328 metastatic lymph nodes; from the 2nd to the 13th groups of lymph nodes, the 10th (15.60%, 44/282), the 11th (22.79%, 98/430), and the 12th to the 13th (15.25%, 61/400) groups had the highest lymph node metastasis rate. Multivariate analysis showed that maximum tumor diameter ( OR=2.71, 95% CI: 1.82-4.09, P<0.001), CT imaging features ( OR=2.49, 95% CI: 1.59-6.99, P=0.001), degree of differentiation ( OR=2.06, 95% CI: 1.11-3.81, P=0.010), serum carcinoembryonic antigen (CEA) ( OR=1.87, 95% CI: 1.42-2.58, P=0.015), and pleural invasion ( OR=1.81, 95% CI: 1.07-3.07, P=0.021) were all independent influencing factors for the occurrence of lymph node metastasis in Ⅱa NSCLC patients. The C-index of the training set and the validation set were 0.91 (95% CI: 0.88-0.97) and 0.89 (95% CI: 0.84-0.96), respectively, and the calibration curves of the two sets were well fitted to the ideal curves. Receiver operating characteristic curve analysis showed that, the area under curve of the nomogram prediction model used for differential diagnosis of patients in the training and validation sets were 0.92 (95% CI: 0.87-0.96) and 0.91 (95% CI: 0.85-0.98), respectively. There were statistically significant differences in surgical time [(203.08±38.26) min vs. (177.14±22.18) min, t=5.59, P<0.001], intraoperative blood loss [(458.14±65.04) ml vs. (426.08±26.58) ml, t=4.34, P<0.001], thoracic drainage volume [(1 200.14±226.58) ml vs. (1 114.38±164.34) ml, t=2.92, P=0.004], extubation time [(6.57±1.28) d vs. (5.02±1.12) d, t=8.71, P<0.001], hospital stay [(15.02±1.29) d vs. (12.08±1.57) d, t=13.86, P<0.001) between the SML group and the LSND group in the training set. There was no statistically significant difference in OS rate between two groups of patients at 1 year (96.77% vs. 96.67%), 3 years (84.95% vs. 86.67%), and 5 years (75.27% vs. 77.78%) ( χ2=0.16, P=0.689). There was a statistically significant difference in the overall incidence of adverse reactions [18.28% (17/93) vs. 7.78% (7/90) ] between two groups of patients ( χ2=4.43, P=0.035) . Conclusion:Intrapulmonary segment lymph node accounts for a considerable proportion in the metastasis process of NSCLC, with the highest degree of lymph node metastasis rate in groups 10, 11, and 12-13. Maximum tumor diameter, CT imaging features, degree of differentiation, serum CEA, and pleural invasion are all independent influencing factors for the occurrence of lymph node metastasis in NSCLC patients. Compared with SML, LSND has less trauma and a lower incidence of adverse reactions.