Abstract: In this paper, we presented that the obvious differences between the fracture angle of the complex fatigue crak and that of the brittle fracture crack are not only superficial but also substantive,especially in some particular crack states,for instance, some fatigue cracks don’t propagate along the direction of their original cracks in the condition of pure type I （K₁₁=0）.On the contrary, they do so in the condition of complex type （K₁₁≠0）. Besides, the growth rates da/dN of the crack between complex fatigue and pure type I fatigue have different regularities. It appeared that their criterions shoudn’t be identical.