A supersonic jet is utilized in industries to cool a heated material, to blow the dust away from the product and so on, and also used as propulsion of space vehicle in aviation field. The jet is usually underexpanded or overexpanded, having a cell structure. When the jet impinges on materials, the jet oscillates itself and a noise radiates from it. In this paper, the underexpanded jet impinges normally on a thin plate, and oscillation of the jet and vibration of the plate were analyzed at different nozzle-plate spacings. The flow fields between the nozzle and the plate with various thicknesses were compared with each other. As a result, an effect of the flow pattern of the impinging jet was found on the vibration of the elastic plate.