The past Results of researchers who had shown postoperative radiation therapy (PORT) for patients with pN2 non-small cell lung cancer have been inconsistent in previous research. Researchers postulated that PORT could increase overall survival (OS) in stage N2 non-small cell lung cancer patients with an elevated lymph node ratio (LNR).  Adjusted by patient characteristics and treatment information, the effect of PORT and LNR on OS was evaluated using Cox models. PORT was present in 1,728 of 4,050 patients (42.7%). The more recent period saw a rise in IMRT usage (53.8% from 2010-2016 compared to 24.0% from 2004-2009). In the entire cohort, those with PORT had longer OS. With PORT, patients with insufficient lymph node dissection (LND) had a little increase in overall survival (HR=0.91, P=0.058). Patients with LNR less than 15% (HR=1.11, P=0.21) or LNR 15-29% (HR=1.03, P=0.73) saw no improvement in OS with PORT, but those with LNR of 30% saw a substantial improvement in OS (HR=0.83, P=0.006). While 3D RT did not enhance OS (HR=0.89, P=0.32), IMRT considerably did in patients with LNR, more than equal to 30% (HR=0.75, P<0.05). Patients with pN2 NSCLC who underwent R0 resection, appropriate LND, and significant LNR had longer survival rates when PORT was used. Overall, patients with poor LND, high LNR, or IMRT use accounted for most of the PORT-driven OS improvements.