An HTTP-based synchronization method includes obtaining a first response sent by a source server or a cache in response to an HTTP request for obtaining a file; determining time when the first response is sent in local time at server, according to a value of a Date field and a value of an Age field in the first response; determining time when the first response is sent in local time at client, according to the client time of an event related to the first response; and determining time offset between the server time and the client time according to the time when the first response is sent in local time at server and the time when the first response is sent in local time at client, and setting up a synchronization relationship between the client time and the server time.