In this paper a physical model for CPM-MQW-LD mode-locking process is presented. In the model, the saturable absorbing effect of the absorber and the effect of the transient grating are considered. In addition, the transient gratings occuring at the both facets of the LD and in the gain region near the absorber are also analyzed. As an example, the MQW-LD mode-locking process and the effect of transient grating on laser pulses FHPW and on the peak power are studied.