Abstract: The crosstalk coupling of nonuniform transmission lines is analyzed using the finite difference time domain method. Based on the scattering of thin wire, the ladder model is adopted to approach the nonuniform transmission lines. Four cases of unequal length lines, inconsistent line diameters, nonparallel lines and cross lines are analyzed. The simulation results indicate that the crosstalk coupling has little influence by the unequal length lines or lines diameter, but great influence by the angle of nonparallel lines or cross lines.