Surface wave speed is measured in a two-layer gelatin phantom in water on three different surfaces with a scanning ultrasound transducer. The gelatin concentrations of the two layers of the phantom are 15% and 10% and the three surfaces are the two outside surfaces of the 15% and 10% layers and the interface between the two. The speed measured on the outside surface of the 15% layer is faster than on the 10% layer, but both of them are slower than the surface wave speed measured on the interface surface. The relationship between the surface wave speeds on the two outside surfaces can be explained by the different gelatin concentrations. The wave speed on the interface surface is the fastest among the three surfaces and may be explained by the Stoneley wave theory. The study is meaningful for understanding the acoustic wave propagation on the surface of internal organs such as heart, kidney and lungs.