Abstract: The invention relates to a method for back tracing an authentication status implemented in a hierarchical intermedia architecture, where a RADIUS server is sequentially connected to at least one intermedium by means of a hierarchical connection, each intermedium is connected to at least one end point respectively, the hierarchical intermedia architecture utilizes a hierarchical back trace protocol packet, so that when each end point finds that it does not pass an authentication the end point can issue the protocol packet for requesting the intermedia to back trace nodes in the hierarchical intermedia architecture sequentially and commanding the intermedia to send information back to the end point for identifying the status and errors of the intermedia.