Abstract: The four point flexural fatigue curves of the QSS400 steel including initial hot rolled plate and hot pressed shell at 800 ℃ were measured under asymmetry circle-load conditions with stress ratio of R=-0.8.The effect of hot pressing on microstructure and fatigue property of QSS400 steel was investigated.The results show that the recrystallization of QSS400 steel hot pressed at 800 ℃ took place but the microstructure of the steel didnt become coarsened and still kept fine grain degree of grade 11 due to the addition of Nb which restrained the forming of carbide.However,the fatigue strength decresed slightly,just about 4%.