A novel process named Expansion non-equal channel angular extrusion (Exp-NECAE) is proposed, which integrates various deformations including upsetting, shearing and extrusion in a single pass. Based on the theoretical analysis, severe plastic deformation behavior of commercially pure aluminum under multi-deformation coupling effects was investigated by numerical simulation and experimental verification, and the evolution of microstructure and mechanical properties of the processed materials was discussed. The results show that Exp-NECAE process has the advantage of high efficiency as a compound deformation method, the billet was extruded continuously, stably and compatibly, and the deformation process can be classified into three different stages: corner area deformation, transition area deformation and extruded area deformation, respectively. During the process, the processed material was in an ideal three-dimensional compressive stress state with homogeneous deformation distribution. The accumulative strrain was as high as 2.56 after a single pass of extrusion, which was close to the theoretical calculation. After one pass of Exp-NECAE, under the simple shear strain induced by the coupling effects of upsetting, shear and extrusion, the grain size of commercial pure aluminum was significantly refined, forming a mixed microstructure dominated by ultrafine equiaxed grains with an average grain size of around 2.73 μm. Moreover, the mechanical properties of the processed material were significantly improved. The average microhardness was 55.8 HV, and the tensile strength and the elongation can reach up to 161.2 MPa and 13.9%, respectively. A large number of small and deep dimples were observed in the fracture morphology, and the distribution was relatively uniform, showing a good ductile fracture characteristics.