A field experiment was conducted to investigate the spatial distribution of weeds at the Sari Agricultural Sciences and Natural Resources University in 2011. Field was divided into 42 grids (1.5×1.5 feet) then all samples were taken from grids intersection points before corn planting, after harvesting and ear emergence stage. Weed maps and semi variance analysis carried out using RW99 and Gs+ softwares. The results showed that the highest amount of weed population belongs to prostrate pigweed, nutsedge and redroot pigweed, respectively. There was a strong and moderate spatial correlation as spherical and exponential variograms model at all stages of sampling. The seed banks were patches with different sizes and densities. Seed bank patchy pattern at the beginning of season was in accordance with seed bank at the end of season. Knowing the seed bank density, we can forecast weed seedling density during crop growing season.