A method and device including modules for performing a statistics on a resident time span ratio of a dual-mode single-standby terminal user in dual networks, including: setting a Tstart, a Tend and a period t; with respect to a network of each mode in the dual networks respectively, acquiring a periodic location update times, periodic routing area update times, call time span except periodic location update and periodic routing area update, number of starting-up users, T3212 and T3312 of said user in each period t within a time slice from the Tstart to the Tend; according to the parameters, calculating resident time spans of each user in dual domains or CS single-domain network in an idle state, in PS single-domain network in the idle state, and in a connection state, and obtaining the respective resident time spans, thereby the resident time span ratio, of each user in the dual networks.