The change in the microstructure of granular materials under a biaxial loading condition was investigated by numerically simulating an idealized assembly of two-dimensional particles. The distinct element method was employed for simulating an idealized assembly. Local strain increments were calculated from relative displacements of particles within triangle elements which were defi ned by particle centers. The obtained local strain increment was analyzed from spatial statistical point of view. The coeffi cient of spatial autocorrelation of the local strain increment distribution was calculated to estimate the intensity of spatial dependence of the local strains in the entire area of the specimen. The spatial analysis results indicate that the range of autocorrelation designating the range of the presence of spatial autocorrelation increased during the biaxial compression loading. This variation of the range of autocorrelation implies that the spatial microstructure of granular materials varies throughout deformation processes.