Abstract: In this paper we present a relation for the bulge effect factor of declivous cracks.With this relation,the calculated demolition load and cracking load are in line with their corresponding experimental results,the average error being about 8%.The said relation is therefore good for engineering practices.The law of declivous fatigue crack growth is examined,using direct method and projective method to define the stress intensity factor at the top of a declivous crack after fatigue growth.Pursuing the Paris relation for crack growth rate in processing the data,we have obtained a crack growth rate formulation for 18MnMoNb steel.The fatigue growth angle of declivous crack is also discussed.