Four kinds of improved genetic algorithm are designed in this paper combining the standard genetic algorithm with the hierarchical strategy and the idea of simulated annealing. They are namely hierarchic genetic algorithm, simulated annealing genetic algorithm and simulated annealing hierarchic genetic algorithm. The availability and the validity of these algorithms have been verified by the calculation results. The further performance analysis of the algorithms proves that not only the global convergence but also the genetic evolution speed are improved through the modified algorithm introduced in this paper.