To study the change of grain size for the hot extrusion deformation of half shaft bushing,according to the dynamic recrystallization theory,the paper establishes the dynamic recrystallization model of material and uses the finite element analysis software Deform-3 D to study the shape of half shaft bushing in the mold work under the condition of different variation of hot extrusion deformation process of material grain size. The results show that while doing the extrusion in the shape of straight line and circular arc and spline curve with three kinds of work,the grain sizes are at different levels of detail. The circular mold material makes grain size smaller and more symmetrical. The result has important significance on the improvement of performance and quality of the sleeve.