Abstract: This paper formulated a priority queuing model for the periodical inband sensing mechanism. On the basis of the analysis of this model, in which the idle time of the secondary user is lack of utilization, the paper proposed an idle time based inband proactive sensing strategy (ITIPSS). In addition to executing periodical inband sensing, ITIPSS uses the idle time gaps of the secondary user to detect the primary’s return proactively. The simulation results show that ITIPSS can shorten the detection delay to the primary user significantly and improve the protection of the primary user efficiently.