Abstract: Using the transmission dynamics model, the number of confirmed cases, cured cases and dead cases announced by the National Health Commission, we got the following three conclusions: First, the joint prevention and control mechanism adopted by the Chinese government has played a very significant role in the prevention and control of Corona virus diseases 2019 (COVID-19). The basic regeneration number (R_0) in Hubei province has gradually decreased from 3.86 before February 3 to 0.42 after February 8; and R_0 of Zhejiang province, Guangdong province, Henan province, Hunan province, Jiangxi province, Anhui province, Beijing city and Shanghai city (six provinces and two cities) decreased from 3.68 before January 30 to 0.18 after February 4. Second, the infectivity of asymptomatic and symptomatic cases was almost the same before confirmed diagnosis. The difficulty in the prevention and control of the COVID-19 lies in the isolation and timely treatment of asymptomatic cases. Although the number of asymptomatic cases in Hubei province has gradually dropped from 23,068 to 2,935 on February 29, the situation of epidemic prevention and control in Hubei province remains very grim. The number of asymptomatic cases in six provinces and two cities has fallen to between 5 and 21 on February 29, and the epidemic of COVID-19 in these regions has been effectively controlled. Third, selecting the time to relax traffic control measure in Hubei province requires caution. The transmission dynamic model predicts that if the traffic control measures are lifted in mid-May or mid-June, and approximately 100,000 asymptomatic cases are allowed to be imported from Hubei province to six provinces and two cities, the cumulative number of infected people will increase by 5.5 or 1.3 after 1.5 months. However, if the traffic control measures are lifted in mid-March or mid-April, the cumulative number of infected people will increase by 93 or 22 after 1.5 months.