The embodiment of the invention discloses a charging method, comprising the steps of: a first network side device receiving a first call request, and determining the type of a calling user according to the first call request, wherein the first call request at least carries a calling number and a called number; when the calling user is a CS user, determining whether to perform long distance charging on a called user according to whether the called number carries a first callflag; and when the calling user is an IP IMS user, determining whether to perform long distance charging on the called user according to whether the access place of the calling user is inconsistent with the place where the first network side device is located. The embodiment of the invention also discloses a charging system and a network side device. The charging scheme of the embodiment is suitable for a group client to directly connect with an IMS domain through an ISBC in an SIP (Session Initiation Protocol) mode, can be applied to various user services, and has the characteristics of accurate charging and wide application range.