Hypersonic overflow cooling is a new type of aircraft thermal protection method. The basic idea is that the overflow hole is arranged in the high heat flux area, and the coolant poured out in an overflow way.The liquid film spreads through the aircraft surface friction forming a thermal buffer layer to reduce the surface heat flux. Now, the overflow cooling technology is still in the exploratory stage, and a large number of experimental verification and mechanism research work need to do. In this paper, wind tunnel experiment platform for overflow cooling was build, adopting the heat flux measurement, liquid film thickness measurement and liquid film motion observation technology. The feasibility of applying overflow cooling to hypersonic thermal protection was verified, and the characteristics of liquid film flow under hypersonic flow field were preliminary analyzed. Reserch results show that: (1) In hypersonic flow field, the liquid film can be formed on the vehicle surface , and effectively isolate the external high temperature air to reduce the surface heat flux; (2) On wedge surface, the leading velocity of the liquid film gradually decelerate. Increase coolant flow rate, the liquid film thickness change is not obvious, but the leading velocity of liquid film will increase; (3) Surface waves exist in liquid film, and evolve in time and space direction, which leads to slight perturbation of liquid film thickness; (4) There is a lateral expansion phenomenon in the liquid film layer, that is, the width of the liquid film is greater than that of the overflow hole. The reason is that the liquid film layer don’t match the flow field boundary condition, and there is pressure gradient, forcing the coolant to flow to low pressure area, thus broadening the liquid film layer.