The attenuated total reflection technique was used to excite surface plasmon. We have measured the efficiencies of the surface plasmon energy emitted through surface roughness into air side, for prism/LB film or Ag film /Ag film/ air and prism/Ag film/air structures. Depending on the distribution of scattering light intensity, the surface roughness parameters, i. e. the transverse correlation length σ and the surface corrugation depth δ of air/Ag film interface were simultaneously evaluated. Then we calculated the emission efficiency of the surface plasmon polariton energy from σ and δ. The calculated efficiency corresponds with that of experiment.