Equal channel angular pressing (ECAP) is an innovative processing procedure in which a material is subjected to intense plastic deformation without changing the cross-sectional dimensions of the work-piece. The deformation is achieved by simple shear when pressing the work-piece through a special die containing two channels, equal in cross section, intersecting at an angle of. Extensive reports have revealed that ECAP is a prospective industrial application technology for producing bulk materials with ultra-fine grains. Since the deformation during equal channel angular pressing is achieved by simple shear, quantitative analysis of simple shear is essential for understanding the process. In this investigation, simple shear during equal channel angular pressing experiment on pure aluminum work-piece was measured and analyzed. The results were validated using analytical and finite element modeling methods. The results showed that the analytical and finite element modeling methods on simple shear deformation matched well with experiment results for metallic materials. An overall picture of plastic flow during ECAP is helpful to promote the application of this new technique.