Abstract: A load balance model LOBAC for NOWs is presented in the paper, in which a NOW system is organized into hierarchical clusters, and applications are scheduled by a hierarchical scheduling policy. Based on the unit of clusters instead of nodes, LOBAC takes two stage scheduling to balance loads among clusters. The load balance algorithm is easy to implement, and needs less overhead. It can balance the loads fast in the whole system and provide better performance. It can also be adapted to large scale systems very well.