This study evaluates the effectiveness of non-pharmaceutical interventions (NPIs) in containing the COVID-19 outbreak in China. Using epidemiological and anonymized human movement data, the authors developed a travel network-based stochastic susceptible-exposed-infectious-removed (SEIR) model to simulate different outbreak scenarios and intervention timings. The model estimated that as of February 29, 2020, there were approximately 114,325 COVID-19 cases in mainland China, with 85% in Hubei Province. Without NPIs, the number of cases would have increased significantly by February 29, 2020. The early detection and isolation of cases were found to be more effective than travel restrictions and contact reductions, but combined NPIs achieved the strongest and most rapid effect. The lifting of travel restrictions since February 17, 2020, did not lead to an increase in cases if social distancing interventions were maintained. The findings highlight the importance of early and integrated NPI strategies and provide guidance for other regions to contain the spread of COVID-19.This study evaluates the effectiveness of non-pharmaceutical interventions (NPIs) in containing the COVID-19 outbreak in China. Using epidemiological and anonymized human movement data, the authors developed a travel network-based stochastic susceptible-exposed-infectious-removed (SEIR) model to simulate different outbreak scenarios and intervention timings. The model estimated that as of February 29, 2020, there were approximately 114,325 COVID-19 cases in mainland China, with 85% in Hubei Province. Without NPIs, the number of cases would have increased significantly by February 29, 2020. The early detection and isolation of cases were found to be more effective than travel restrictions and contact reductions, but combined NPIs achieved the strongest and most rapid effect. The lifting of travel restrictions since February 17, 2020, did not lead to an increase in cases if social distancing interventions were maintained. The findings highlight the importance of early and integrated NPI strategies and provide guidance for other regions to contain the spread of COVID-19.