From the point of view of the average compressibility and density, and based on the theory of multiple scattering, the effects of superleak grains on the propagation of the 4th sound in liquid helium Ⅱ have been dicussed. The formulas of the index of refraction both (6) and (31) are obtained. The results of numerical calculations show the role of the former is negligible but the variation of 4th sound velocity due to the multiple scattering agrees well the experimental values given in the literature.