The microscopic plastic deformation behavior of aluminum sheet during uniaxial tension is experimentally investigated by a confocal laser-scanning microscope. The surface roughening is closely related to the inhomogeneity of polycrystalline metals, that is, to the inhomogeneous plastic deformation of respective grains. In order to clarify the deformation behavior of polycrystalline metals, new measuring methods and 4 types of strains of grains are introduced and inhomogeneous of strain of grains are investigated. Digital image processing technique is applied to the surface image taken by the CCD camera for measurement. It is shown that the grain-area strain, the maximum dimension and mean dimension strain, the grain-boundary length strain and the standard deviations of these parameters statistically increase in proportion to the applied strain. Discussions are made on the differences between these measuring methods of strain parameters of grains, variations of measured statistical results including comparison with equilateral polygon model during tensile deformation.