There has been no previous study on the efficacy of the thoracic radiotherapy (TRT) in oligometastatic or polymetastatic extensive stage small-cell lung cancer (ES-SCLC) to the overall survival (OS). In a group of 270 ES-SCLC cases retrospective study, 78 patients (28.9%) had oligometastases and 192 (71.1%) had polymetastases, among which 51 oligometastatic patients (65.4%) and 93 polymetastatic patients (51.6%) received TRT. Propensity score matching (PSM) was utilized. The 2-year OS, progression free survival (PFS) and local control (LC) in oligometastatic and polymetastatic patients were 22.8% and 4.5% (p < 0.001), 12.0% and 3.8% (p < 0.001), and 36.7% and 6.1% (p < 0.001), respectively. The 2-year OS in oligometastatic patients with the chemotherapy + radiotherapy and chemotherapy alone were 25.2% and 12.7% (p = 0.002), in contrast to 10.0% and 6.8% (p = 0.030) in polymetastatic patients. The estimated hazard ratios for survival were 2.9 and 1.7 for both oligometastatic and polymetastatic patients with radiotherapy. The polymetastatic group has a lower LC (6.1% v.s. 36.7%, (p < 0.001)), due to polymetastases patients receiving involved-sites radiotherapy with low dose schemas. TRT improved OS of patients with oligometastases and polymetastases. Our study demonstrated that aggressive TRT might be a suitable addition of chemotherapy when treating ES-SCLC patients with oligometastases and polymetastases.