In this paper, we consider the problem of quality of service (QoS) provisioning for K users sharing a downlink wireless channel. The channel to each user is assumed to be a block Rayleigh fading channel. We develop simple and efficient scheduling schemes which can yield substantial capacity gain. Our approach is to maximize the throughput in subject to a given delay QoS constraint by choosing the appropriate number of users served in a frame (or a coherent duration). We call this number the degree-of-multiplexing (DoM). By analysis of the effective capacity, we investigate the effect of DoM on QoS performance in wireless multiuser scheduling. Finally, numerical investigation shows that the analytic results make asymptotically an match with the simulations, and the comparative superiority of our approach to the previous ones is discussed.