An embodiment of the invention discloses a video access control system based on an IP (Internet Protocol) multimedia subsystem and a service processing method. According to the invention, an HSS (Home Subscriber Server) is pre-configured with private identification PVIs for all access control users, and an implicit registration set of the HSS comprises a first public identification used for access control service and a second public identification used for communication service. An access control outdoor unit is used for receiving access control service call requests, requesting the first public identification corresponding to the called room numbers from a number translation table and sending calling requests through an IMS network by taking the first public identification as called numbers. An access control indoor unit is used for identifying formats of the called numbers in the calling requests and starting a video access control function interface for allowing the video access control service between the indoor access control unit and the outdoor access control unit if the format the called numbers is an access control number format or starting an audio/video communication function interface for allowing the communication service if the format of the called numbers is a public phone number format. According to the embodiment of the utility model, the access control service and the communication service can share one terminal while mutual influence on functions is avoided.