In event-driven wireless sensor networks, many redundant packets flow from monitored sites through the network and to the sink, resulting in a typical funnel effect which affects event reliability, negatively. Taking this transport property into account, a differentiated priority queue management scheme is presented, in which the packets with same event identification are prioritized according to their arrival sequence, and scheduled differentially. The queue model, packet prioritization strategy and event table maintaining methods are examined in detail. Simulation results show that the queue management scheme can improve event reliability of event-driven sensor networks in terms of event detection ratio, accuracy ratio, and event delay efficiently.