Through the Stokes models of devices with polarization-dependent loss(PDL) was proposed,the impact of PDL on the state of polarization(SOP) of optical signals in the optical fiber communication systems was investigated.The results of computer simulations show that the PDL give rise to the direct influence on the degree of polarization(DOP) and intensity of optical signals when the DOP of input optical signals less than unity.However,the DOP of the output optical signals are not varied at all and the SOP of output optical signals are changed rapidly when the DOP of input optical signals are equal to unity.