A new process named equal channel angular extrusion with spherical cavity (ECAE-SC) is proposed based on the idea of breaking through the equal channel during the whole process of traditional ECAP, which combines positive strain with shear strain. On the self-designed ECAE-SC die, the continuous, efficient and compound severe plastic deformation of commercially pure aluminum was realized in a single pass of ECAE-SC at room temperature. Microstructure evolution of commercially pure aluminum during ECAE-SC process was observed and analyzed by optical microscopy (OM), EBSD and TEM. Moreover, microhardness of the processed materials at different deformation regions was tested. The results show that under the severe plastic deformation induced by simple shear, the equiaxed ultrafine grains with average grain size of 400 nm can be obtained by only one pass of ECAE-SC. The deformation mechanism of ECAE-SC at room temperature is dominated by dislocation slip accompanied with incomplete continuous dynamic recrystallization, and the grain refinement process mainly includes the generation of shear bands, the formation of cellular substructures, the appearance of subgrains with low angle boundaries (LABs) and the formation of equiaxed ultrafine grains with large angle boundaries (HABs). After one pass of ECAE-SC, the main texture of commercially pure aluminum is Gauss texture {110} < 001 >, while some {111} < 112 > copper texture exists. The microhardness of the processed materials on the cross section increases significantly, and the average value increases from 28.94 HV to 56.53 HV, with an increase of 95.33%. Meanwhile, a more uniform hardness distribution is obtained.