Using the Multiple Important Sampling（MIS） technique

the performances of 10 Gbit/s optical communication systems affected jointly by Polarization-Mode Dispersion（PMD） and Polarization Dependent Loss（PDL） are simulated under different initial pulse chirps and duty cycles.The power penalty distribution and system outage probability of the system modulated by On-Off Keying（OOK） and Differential Phase Shift Keying（DPSK） are given when PMD=10 ps and PDL=1 and 1.5 dB.It is found that the system performance obviously varies under different duty cycles and the introduction of proper initial chirps

e.g.C=0.5

is conducive to the enhancement of the system performance.