采用有限差分法原理对方形同轴线进行研究，计算分析了方同轴线TM波的两个最低模式的色散特性以及其横截面的场分布。利用Matlab编程得到了方同轴线中TM波两个最低模式的色散曲线，横截面的电磁场分布，并将所得到的结果与仿真软件得到的结果相对比，以验证所编写程序的正确性和有限差分法的适用性。-Finite difference method using the principle of the square coaxial study, calculate and analyze the dispersion characteristics of Square Coaxial TM wave of the two lowest modes as well as its cross-section of the field distribution. Use Matlab programming dispersion curves obtained in the square coaxial TM wave the two lowest modes, the cross-section of the electromagnetic field distribution, the results and the results obtained with the simulation software was compared, and to verify the correctness of programming the applicability of the finite difference method.