Objective To find out the transmission chain of COVID-19 epidemic in a bus in Chongqing City with the technical support of big data. Methods Through the field epidemiological investigation method,combined with cases’ activity trail comparison and surveillance video analysis,the cases and close contacts were investigated,respiratory tract and stool specimen were collected,and real-time fluorescent RT-PCR was used to detect novel coronavirus nucleic acid. Results A total of 3 cases were found in the cluster epidemic,including 2 severe pneumonia cases and 1 common pneumonia case,all of which were cured.Case No.1 was an imported case from Wuhan City of Hubei Province,and took the bus with case No.2 for 30 minutes on the day of onset.During this period,case No.1 took off the mask for 10 minutes,case No.2 did not wear the mask,and case No.3 was a family member who lived with case No.2.The respiratory specimens of case No.1 and case No.3 were positive for novel coronavirus nucleic acid.For case No.2,the nucleic acid of novel coronavirus was negative in four consecutive respiratory specimens and positive in the fourth fecal specimen. Conclusion Novel coronavirus has strong transmission ability,and the transmission risk is high in confined spaces,such as bus.The application of big data technology plays an important role in epidemiological investigations.The stool specimen is another biological sample for the discovery of novel coronavirus infection.