Abstract Purpose The gross tumor volume (GTV) could be an independent prognostic factor for unresectable locally advanced non-small cell lung cancer (LANSCLC). We aimed to develop and validate a novel integrated GTV-TNM stratification system to supplement LANSCLC sub-staging in patients treated with concurrent chemoradiotherapy (CCRT). Methods We performed a retrospective review of 340 patients with unresectable LANSCLC receiving definitive CCRT. All included patients were divided into two randomized cohorts. Then the Kaplan–Meier method and Cox regression were calculated to access the prognostic value of the integrated GTV-TNM stratification system, which was further validated by the area under the receiver operating characteristic curve (AUC) score and F1-score. Results The optimal outcome-based GTV cut-off values (70 and 180 cm 3 ) of the modeling cohort were used to determine each patient’s integrated GTV-TNM stratum in the whole cohort. Our results indicated that a lower integrated GTV-TNM stratum could had better overall survival and progression-free survival (all P  < 0.001), which was recognized as an independent prognostic factor. Also, its prognostic value was robust in both the modeling and validation cohorts. Furthermore, the prognostic validity of the integrated GTV-TNM stratification system was validated by significantly improved AUC score (0.636 vs. 0.570, P  = 0.027) and F1-score (0.655 vs. 0.615, P  < 0.001), compared with TNM stage. Conclusions We proposed a novel integrated GTV-TNM stratification system to supplement unresectable LANSCLC sub-staging due to its prognostic value independent of TNM stage and other clinical characteristics, suggesting that it could be considered in individual treatment decision-making process.