Background: Lung cancer represents a significant global health burden, with non-small cell lung cancer (NSCLC) being the most prevalent form of this disease. While surgery remains the cornerstone of treatment for early-stage NSCLC, patients with locally advanced or inoperable NSCLC require alternative therapeutic strategies. Purpose: to assess the long-term survival data and determine the associated factors impacting survival outcomes for patients with locally advanced unresectable non-small cell lung cancer (NSCLC) treated with radiotherapy. Methods: We retrospectively analyzed patients diagnosed with inoperable stage III of NSCLC who received radiation therapy at Hospital 175 from January 2019 to June 2022. The patients had a performance status score (PS) of 0-2 and only one primary lung tumor. We collected patients' background information, including age, gender, pathology, TNM, combination chemotherapy, PET/CT characteristics, and radiotherapy plan parameters. All patients received radiotherapy, at a dose equivalent to 60Gy or more. During radiation therapy, patients were monitored for radiation toxicity. We used the Kaplan-Meier method to estimate overall survival (OS) rate and the Cox regression model to identify the risk factors affecting the treatment outcomes. Results: A total of 240 cases, male: 75%, PS 0, 1, 2 respectively: 24%, 72%, 4%. Histopathological types: squamous cell (9%), glandular cell (83.5%), others (7.5%). Which, subgroups of stages IIIA, IIIB, and IIIC: are 32%, 48%, and 20%. The rate of patients having chemotherapy before radiation was 80.3%, and having PET/CT scans was 43.5%. Patients with radiation alone: 73.4% and concurrent chemoradiotherapy: 26.6%. Median follow-up time: 16.3 months, median OS: 19.5 months. OS rates after 1, 2, and 3 years are 76.2%, 38.8%, and 27.4%, respectively. The most common toxicity was grade 2 esophagitis. Patients who received concurrent chemoradiotherapy had a better prognosis than those who received radiation therapy alone. Regimen of radiation therapy, age, histopathological type, and lymph node metastasis were significant factors affecting overall survival outcomes. Conclusions: Radiotherapy is an essential part of treatment for inoperable NSCLC. The best survival benefit is achieved with concurrent chemoradiotherapy. Besides, age, lymph node metastasis, and histopathological type are also potential factors that can influence patient outcomes.