The invention provides a method and system for tracking the source of a user. The method includes the steps that an access log sent by a broadband remote access server in the process that the user has access to a target webpage is received, wherein the access log at least contains a user account, access time, a public network IP address and a public network port block of the user and address information of the target webpage; a source tracing request sent by source tracing equipment is received, wherein the source tracing request contains access time, a public network IP address, a public network port number and the address information of the target page; according to the access time, the public network IP address, the public network port number and the address information of the target webpage contained in the source tracing request, the corresponding user account is acquired from the access log, and then the source of the user can be traced. According to the method and system for tracking the source of the user, the address information of the target webpage is added into the access log, the source of the user is traced through the query for the condition of the access log, and therefore the user source tracing complexity is reduced, and the user source tracing efficiency is improved.