Abstract: The normal stress intensity factor ratio criterion forpredicting cracking initiation and cracking direction of the mixed modefracture of fiber composites is proposed. In the criterion theeffects of both normal stress intensity factor and shear stressintensity factor are taken into consideration. In using the criterionit is not necessary to determine the characteristic dimension r_0 ofthe material in the vicinity of crack tip, so it is quiteconvenient and can yield good results.