Statistical characteristics of polarization mode dispersion (PMD) are investigated with dynamical equation. Simulations are performed in two methods: statistical ensemble and frequency ensemble. It is shown numerically that the results from the two methods are consistent with each other. Limited by the condition of long normalized distance, the square of rms delay grows linearly with normalized distance; the probability density functions (PDF) of PMD vector′s components obey Gauss distribution and the PDF of differential group delay (DGD) time obeys Maxwell distribution; PMD vectors are dispersed on the whole Poincare sphere.