A complete and accurate statistical analysis of cases of contraction with SARS-CoV-2 are given under the conditions of strict mandatory quarantine and isolation and of a high rate of full vaccination[i]. Sars-Cov-2 is still new, and little is known about either its direction of variation or its propagation laws. China has been attacked by its largest outbreaks of COVID-19 since March. Pervasive arguments arose among people in China and around the world. Here we reveal the essential reasons why China has been and will be adhering to its “dynamic zero-COVID policy” which stands in contrast to a global trend towards easing restrictions and attempting to co-exist with the circulating virus[ii], including the choice uniqueness, morbidity differences in different cities, unpredictability, worries of sudden impact to medical system, successful reducing to zero the number of each active chain of transmission and outstanding economy achievements, etc. This study provides first-hand valuable information for further research on similar epidemics in the future. It may bring new thoughts for correction of present epidemiological theory and mathematical models, as well as new theoretical supports for the prevention policy making. It may also give other countries time to be better prepared for the coming 6th wave driven by Omicron BA.2.