Abstract: Fine aluminium was extruded by using self-developed continuous variable cross-section extruding equipment, and the microstructure of samples was studied. The results showed that the grain size is different in every section along the extruding direction owing to the different extrusion rate. The grain size is fined with increasing extrusion rate. The phenomenon is more obvious in a sin-gle cross-section extruded sample. The grains on the same section are not nonuniform. In the same section, the grain size is increased from outer part to center of the sample. The grains are mostly smaller in the outer part but bigger at the center. Some grains are very big, and the reason is that some grains recrystallize during heat treatment. The research gives the microstructural evolvement rule of extrusions in continuous variable cross-section extrusion.