This study is a double-blind, randomized phase Ⅳ clinical trial in healthy children aged 3-17 years to evaluate the lot-to-lot consistency, immunogenicity and safety of the commercial-scale CoronaVac in healthy children aged 3-17 years .The experimental vaccine was manufactured by Sinovac Research \& Development Co.,Ltd. A total of 2520 healthy subjects aged 3 to 17 years old will be enrolled.The subjects will be randomly divided into 7 groups of 360 participants per group with an equal probability to received 7 batches of commercial-scale vaccine.All subjects received two doses of vaccine on day 0 and day 28.