Abstract: The propagation characteristics of ultrasonic waves on the periodic rough interface between fluid and porous medium are studied, and the effect of porosity on reflection and transmission in the porous medium with open pores and sealed pores is analyzed. Based on Biot theory of porous medium and the grating equation theory, the linear equation including reflection coefficient and transmission coefficient of each order is obtained.. The relationships of porosity with reflection and transmission coefficients of the periodic rough interface are calculated by Fourier transform. The results show that the influence of frequency on the reflection and transmission coefficients is irregular due to the periodic characteristics of the interface. However, the variation of porosity has significant effect on reflection and transmission coefficients. Moreover, the coefficient changes are different in open pores and sealed pores because of the discrepancy in the porous medium states.