At high bit rates fiber transmission systems,polarization mode dispersion(PMD)is considered as the ultimate limiting factor for transmission of information. The pulse root mean square broadening is a main physical variable to judge signal transmission performance. We derive the broadening effects induced by the PMD,and give the exact analytical expressions for the expected pulse broadening in a fiber-optic transmission system suffering from firstorder polarization mode dispersion(PMD). Furthermore,we use the result to calculate the Gaussian pulse.