Abstract: Hot-formed steel is widely used in the automotive industry due to its high strength. This paper takes hot-formed steel as the research object and uses metallographic microscope, scanning electron microscope, transmission electron microscope, uniaxial tensile test and internal friction meter and other testing methods to study the effect of tempering heat treatment on the microstructure, properties and internal friction of 22MnB5 hot-formed steel, and explores the variation law of microstructure, properties and internal interstitial atoms after tempering. The results show that after tempering heat treatment, the tempered martensite structure formed reduces the strength of the hot-formed steel plate, while the elongation after fracture increases. The strength-ductility product reaches the maximum at 200℃ tempering. By comparing the internal friction changes of the quenched state and the 200℃ tempered state, it is found that the Snoke internal friction peak and SKK internal friction peak decrease after tempering, the internal interstitial atoms and mobile dislocation density decrease, and the decrease in solid solution C atom content and dislocation density is also the reason for the decrease in strength.