For the feed-forward polarization mode dispersion(PMD) compensation,it is required to obtain the principal state of polarization(PSP) with high precision.Using a polarization scrambler in the experiment,we obtained the degree of polarization(DOP) ellipsoids from which the information of PSP can be extracted,by the vector algorithm and particle swarm optimization(PSO) algorithm respectively.The results indicate that the vector algorithm obtains more precise(DOP) ellipsoids with faster velocity than the PSO algorithm.The orientation of PSP obtained by the vector alogrithm is with higher exactness than that by the PSO algorithm.Therefore the vector algorithm is shown to be fitter for the feed-forward scheme.