Abstract: In order to improve the strength and toughness of fracturing pump valve body, the effect of different heat treatment processes on the microstructure and mechanical properties of improved 4330 steel are studied. The results show that the strength, toughness of 4330MOD steel can be improved by adding microalloying elements and optimizing the quenching and tempering process. Microalloying elements Nb and V, normalizing and tempering process can reduce grain size and improve strength and toughness. When 4330MOD steel is tempered at 550℃~700℃, the microstructure is tempered sortensite structure, strength decreases with the increase of tempering temperature, toughness increases first and then decreases, tempering strength and toughness match well at 600℃~650℃. Through the addition of microalloying elements and optimization of heat treatment process, the grain size and the width of the strip are small, and the proportion of large Angle grain boundary is high, so as to improve the strength and toughness of the steel.