Patients with extensive-stage small-cell lung cancer (ES-SCLC) have poor prognosis, with limited treatment options. Chemo-immunotherapy is the standard 1st-line therapy for patients with ES-SCLC.When 4 cycles of etoposide+carboplatin (EC) or etoposide+cisplatin(EP) chemotherapy combined with PD-L1 inhibitor are effective, guidelines recommend additional thoracic radiotherapy. In this study, the investigators bring radiotherapy forward, which means that after 2 cycles of EC chemotherapy plus Adebrelimab, participants with response（PR/CR/SD）will receive concurrent radiotherapy and 2 cycles of EC chemotherapy plus Adebrelimab, then maintenance therapy with Adebrelimab （Q3W）. The purpose of this study is to explore the safety and efficacy of Adebrelimab combined with concurrent chemoradiotherapy in untreated participants with extensive-stage small cell lung cancer.