Abstract: The mode I interlaminar fracture toubhness of graphitc bismaleimide composite is investigated in this paper by using the hinge double cantilever beam specimen.Some expressions of interlaminar fracture toughness G_IC are evaluated and compared. The results obtained by methods based on adopting the third polynomial and power function to fit the experimentally measured compliance are satisfactory.The result of test in dicates that the influence of fiber bridging on G_IC of unidirection lamina is obvious.The value of G_IC will decrease twenty percent and the scatter of G_IC will also decrease obviously after cutting bridging fiber by razor blade.In addition,the value of G_IC increases with the increase of specimen thickness.