Abstract: The microstructure and tensile properties of 22MnB5 steel before and after hot stamping at 890 ℃ were studied and compared. The micromorphology evolution during uniaxial tensile of the test steel after hot stamping was investigated by in-situ tensile tests. The results show that the microstructure of the test steel before hot stamping was composed of ferrite and pearlite. After hot stamping, the microstructure changed to martensite, and the strength and the volume of strength and plasticity of the steel increased, while the plasticity decreased. During tensile, the test steel first underwent necking, then the original austenite grain boundaries were destroyed, leading to the initiation of microcracks, and the hole-type cracks were formed by debonding of inclusions. As the tensile continued, the cracks propagated and connected to each other, resulting in the fracture of the steel. A large number of dimples were observed on the tensile fracture surface of the hot stamped test steel, and the fracture form was microvoid coalescence fracture.