This study will enroll patients with limited-stage small cell lung cancer (SCLC). Patients will receive chemotherapy (etoposide and platinum-based drugs) combined with dual immune checkpoint blockade (PD-1/CTLA-4) and thymosin alpha 1, with a total cycles of 4. Thoracic radiotherapy was performed no later than the three cycle of chemotherapy. Prophylactic cranial irradiation was recommended for patients who received complete response or partial response after chemoradiotherapy. Finally consolidation therapy with dual immune checkpoint blockade (PD-1/CTLA-4) and thymosin alpha 1 was conducted for one year. The study aims to evaluate the efficacy and safety of this treatment regimen.