Abstract: The effect of Y-based rare earth on the impact property of 51CrV4 spring steel was studied with the help of SEM to observe the microstructure and the inclusions and morphology of fracture, and by using EDS to analysis the composition of inclusions. The results showed that adding Y-based rare earth can increase impact properties of 51CrV4 spring steel obviously, after heat cheatment, the impact property of 51CrV4 spring steel is increased 68.8%, the fracture morphology transform from quasi-cleavage fracture to ductile dimples fracture, there are large small globular rare earth inclusions in dimple. Adding Y-based rare earth can promote carbide spheroidizing process of 51CrV4 spring steel's tempered microstructure, and make it more diffuse. Y-based rare earth has a good effect on the inclusions in steel by making the inclusions more spherical and smaller.