Objective: To investigate the indoor fine particulate matter (PM 2.5 ) pollution and its influencing factors in children s bedrooms using solid fuel, so as to provide evidence for effective strategy to reduce PM 2.5 pollution. Methods: From December 2019 to November 2020, 198 households (108 in the north, 90 in the south) from two pilots in the north(Jiamusi in Heilongjiang Province) and south of China (Mianyang in Sichuan Province) were selected, and status of solid fuels using were obtained through home visits, dynamic changes in PM 2.5 concentrations in children s bedrooms were monitored by using real time online instruments, and the influencing factors of PM 2.5 pollution were analyzed by using a mixed effects model. Results: During the monitoring period, the daily PM 2.5 concentrations in the northern and southern pilot were 78.33 (40.50, 154.80) and 38.54(26.20, 58.46) μg/m 3, respectively, exceeding standard rates of 44.57% and 33.22%. During the heating period, the daily PM 2.5 concentrations in the northern and southern pilot were 212.50(133.60,244.10) and 104.42(73.97, 134.90) μg/m 3, respectively, with over standard rates of 96.75% and 86.96%. The mixed effects model analysis results showed that children s bedroom PM 2.5 concentrations were associated with solid fuel usage duration, window opening time, room layout (shared entrance door between kitchen and bedroom), indoor smoking, indoor humidity, and solid fuel use in the bedroom ( β =0.19, -0.05, 1.20, 0.43, 0.02, 0.35, all P <0.05). Conclusion Solid fuel combustion significantly comtributes to PM 2.5 pollution in children s bedrooms, with more pronounced impacts observed in northern China compared to southern regions.