Abstract: Polarizationdependent loss(PDL) of optical components is one of the key problems that must be solved to develop the fiber communication． A novel high precision automatic test system for polarizationdependent loss is introduced in this paper. A coupler and optical power meter are employed in the system to realize the measurement of the polarizationdependent loss with a single connection，which can eliminate the effect of system power stability on the test result. In the same system，the measurement for the polarizationdependent loss can be carried out with several methods. With the delay compensation technology of polarization controller, high precision polarizationdependent loss test could be made in all the wave band． Since the wavelength range of the system is 1200～1600 nm, the measurement range of the polarizationdependent loss is 0～5dB and the measurement uncertainty is up to 0.005 dB+PDL×4％, the system can meet the measuring requirement for polarizationdependent loss of every optical component.