Abstract: To understand effect of number and incidence of spur-dikes on flow pattern, flow construction over spur-dikes was studied by flow visualization and light sheet technique in a water channel. There are horse-shoe vortex around spur-dikes and Karman vortices behind spur-dikes. Depending on Reynolds number, flow patterns over spur-dikes can be divided into 4 types: steady single horse-shoe vortex; unsteady single horse-shoe vortex; unsteady double horse-shoe vortices Ⅰ and unsteady double horse-shoe vortices Ⅱ. If number and incidence of spur-dike decrease, intensity of horseshoe vortex and Karman vortices decrease.