EH(extended hypercube) is a kind of topologic architecture to organize large-scale distributed multiprocessor systems. Extended threshold strategy, which uses threshold-length parameter besides threshold, provides a new method to increase the stability in a distributed system. In this strategy, there are many good properties in EH. In this paper, some properties of EH are given at first, then a task allocation algorithm for EH is designed, and finally the performance of this algorithm is discussed in detail.