Objective:To observe the epidemiological characteristics and transmission chain of COVID-19 in Harbin, and to provide epidemiological evidence for improving the COVID-19 preventive measures and optimizing prevention and control strategies.Methods:The epidemic situation of COVID-19 in Harbin in January 2021 was analyzed by using the Infectious Disease Report Information Management System and the Public Health Emergency Management Information System of the China Disease Prevention and Control Information System, the epidemic situation information publicly released by the Heilongjiang Provincial Health Commission, and the epidemiological report of Heilongjiang Province Certer for Disease Control and Prevention and Harbin Center for Disease Control and Prevention. The main transmission chains were sorted out through combination of epidemiological field investigation, serological testing, gene sequencing, big data and other means.Results:From January 12 to February 4, 2021, 295 cases of COVID-19 infection (including confirmed cases and asymptomatic infections) were reported in Harbin, which affected 6 districts of Harbin and were concentrated in 41 of the 274 townships in the city. The sex ratio of male to female was 1.00∶1.12 (139∶156); the age ranged from 1 to 86 years old, and the median age was 45 years old. The proportion of confirmed cases and asymptomatic infection was 1.00 ∶ 1.02 (146 ∶ 149), and there was a significant difference in the distribution of different ages between them ( P = 0.042). The cases were mainly found through the health screening of the centralized isolation personnel (178 cases, 60.3%). Other detection methods included active screening (87 cases, 29.5%), screening of the home isolation personnel (26 cases, 8.8%), and medical treatment in medical institutions (4 cases, 1.4%). The main transmission chain of the outbreak was the case associated with a food processing enterprise, with a total of 259 cases, accounting for 87.8% of the total cases. The gene sequencing results showed that the case sequence was homologous with that of Wangkui County, Suihua City, Heilongjiang Province. Conclusions:A food processing enterprise is involved in the main transmission chain, which indicates that the epidemic prevention and control measures needs to be further optimized. Specifically, the supervision and management of food processing enterprises, cold chain storage companies and other enterprises should be strengthened. High attention should be paid to the hidden dangers of COVID-19 in large and medium sized enterprises with hermetic space in Harbin.