Load balancing has been a key concern for traditional multiprocessor systems. The emergence of computational grids extends this challenge to deal with more serious problems, such as scalability, heterogeneity of computing resources and considerable transfer delay. Due to the dynamic property of grid environment, fixed-parameter prediction model cannot exert its forecast capability completely. To improve the global throughput of computational grid, effective and efficient load balancing algorithms are fundamentally important. A computational grid differs from traditional high-performance computing system in the heterogeneity of computing nodes, as well as the communication links that connect the different nodes together.