Retrieving data from the storage systems with mixed multimedia workloads is a complex process. Different classes of multimedia applications need the storage systems to guarantee different requirements of QoS (quality of service). In order to support as many multimedia applications as possible, the storage systems need an effectual admission control algorithm. A systematic research on this problem is carried on in this paper: the QoS parameters of the multimedia applications are clearly defined, the workload model of aggregate multimedia applications is established, and the constraint condition of admission control is derived. Based on the workload model and the constraint condition, the statistical admission control algorithm is implemented. The simulation experiments show that the novel algorithm is efficient and accurate enough.