In optical Kerr pulse clenear, the used fibers with different mode birefringence degrees can produce different coherent coupling degrees at the two polarization light. Different coherent coupling degrees will affect the output of the optical Kerr pulse clenear. The pulse, spectrum, transmissivity of pulse itself and system with different mode birefringence degrees are simulated. For high birefringence fiber, the coherent coupling effect at the two polarization light can be neglected. For common single mode fiber with medium birefringence degree, the change of pulse′s transmissivity is about ±1%. But for low birefringence fiber, the infection of the coherent coupling is much higher, and the coherent coupling affect also has much higher infection for the temporal and spectral shape and the transmissivity of the pulse itself.