Based on the bistability effect of nonlinear FP cavity (NOLF), a method is suggested to suppress the pedestal of ultra_short optical pulse compressed by dispersion shift fiber (DSF). The coupled mode equation is applied to analyze the chara cteristics of the pedestal suppression of NOLF. The results show that the pedest al energy ratio of transmitted pulse can be decreased to half of incident pulse through reasonably selecting the facet reflectivity of NOLF, the initial phase d etuning between the input pulse and NOLF, and the gain of Er_doped fiber amplifi er.