Flow visualization with surface tufts is carried out to investigate the flow behaviors in two dimensional separated flows over a flat plate. The separation is realized in the channels with diverging cross sectional areas, which are designed to generate constant adversed pressure gradients with quasi one dimensional flow assumption. Distributions of the local flow direction on the flat plate are determined from the photographs of the flow visualization with surface tufts. The flow angles are presented with complex numbers to enable ones to treat them in various manners. Complex correlation factor is introduced to evaluate the three dimensional behaviors of separated flows. The results show the flows immediately downstream of the separation exhibit periodic correlative regions in the spanwise direction as well as in the downstream direction, and their scales are independent of the flow velocity and the magnitude of pressure gradients.