The effects on the wall pressure of the plate caused by the introduction of a gap near the ground and the flaps were investigated experi mentally. The mean pressure on the plate surface was found to decrease with the size changing of the gap near the ground when the gap size (g) is larger than the flap height (h), but the one in the recir culation region increase with the size of the gap when the gap size is about 0<g<2h. Three kinds of now strncture appear with increasing the gap sizes, and the transit point is at g/h-0.2, 0.8 respectively. For the zigzag tlap (d/h=0.19, d is the height of the zigzag), the vmation of wall pressure with g/h is similar to the flat flap in general. The zigzag affects the mean wall pressure in the region of 0<x/h<20 (the i'ecirculation zone) and can decrease the fluctu atthg pressure in the region ofx/h > 20 downstream.