Abstract: Load balancing is a crucial problem in a heterogeneous system such as PC or workstation clusters, which has been widely used in the research and development of numerical weather prediction. A load balancing algorithm, based on feedback, is presented to eliminate the influence of uncertainty of processor speed, which is difficult to measure precisely. The influences of variation of processor speed, load distribution, errors of tested processor speed, etc., have been calculated. The results show that this method is quite robust. The diffusion equation and the simulated physical processes are used to test the algorithm, which shows that it is feasible and can balance the load quite weill.