The invention provides a user tracing method and device and a broadband access server. The method comprises the following steps: receiving a tracing request, inquiring a currently-stored first log record according to the tracing request, and acquiring a corresponding private network IP address, wherein the first log record comprises a public network IP (Internet Protocol) address, the starting port identity and the ending port identity of a port segment corresponding to the public network IP address, a private network IP address, and an allocation time range in which the public network IP address and the port segment are allocated to the private network IP address at the same time; and inquiring a currently-stored second log record according to a tracing time stamp and the private network IP address, and acquiring a corresponding user identity, wherein the second log record comprises the private network IP address, a user identity and a usage time range in which a user corresponding to the user identity uses the private network IP address. Through a scheme, the user is traced effectively and accurately, and the supervision of Internet network security is enhanced.