The disclosure provides a method and a system for realizing application detection and control in an IP-Connectivity Access Network (IP-CAN) session supporting dual stack. The method includes: a Policy and Charging Rules Function (PCRF) informs a Traffic Detection Function (TDF) of an IPv4 address via a TDF session established for the IP-CAN session if a gateway where the PCEF is located or another external network element allocates the IPv4 address according to a request of the UE and the UE accesses a service using the IPv4 address, after the UE establishes the IP-CAN session and accesses a service using an IPv6 address in the IP-CAN session supporting dual stack; and the TDF performs application detection and control on traffic, of which the source address and/or the destination address is/are the IPv4 address, according to an Application Detection and Control (ADC) rule related to the TDF session. With the method of the disclosure, the PCRF will no longer initiate a request for establishing a new TDF session, in this way, the service detection for one same IP-CAN session needs to be reported via one same TDF session only, thus, resources are saved and signalling overhead is reduced.