In this paper, dissipated wave energy, that is, output energy of the wave power device of a shallow-water soliton incident upon the air pump room in the wave power device is obtained by means of theoretical analysis and calculation. In the air pump room, the mass force term in proportion to vertical component of the surface velocity is supplemented to the original Euler equation. Introducing a concept of edge-layer near vertical walls of the air pump room, the matched asymptotic expansion method is applied to obtain uniformly valid solutions throughout the whole region. The matching condition yields a reduced boundary condition to be imposed on the Boussinesq equation in the shallow-water and the air pump room regions extending on the outside of the edge-layer. Solving these Boussinesq equations by means of numerical calculation under the reduced boundary conditions thus led, the dissipated energy characteristic curve of a shallow-water soliton is plotted against the two parameters, that is, nonlinearity a and dept L of the air pump room.