The experiments of the adaptive compensation up to Second-Order in 40 Gbit/ s OTDM System based on degree of polarization (DOP) feedback control are reported. Around the operation wavelength 1560.5 nm of laser source, the DGD and the Second Order PMD decreased obviously after compensation. The effectiveness of the PMD compensator was confirmed by the comparison of eye diagrams, PMD measurement and BER analyses before and after compensation. The particle swarm optimization (PSO) was employed as control algorithm in the Adaptive PMD Compensation system. The compensation time was 30 ms.