Abstract: With more extensive and in-depth application of additive manufacturing in various fields, non-destructive inspection are in growing needs in additive products for its fast and high quality inspection. Porosity is an important factor determining the mechanical properties of the additive products, so it is very important to characterize it during the inspection process. In this paper, the laser power and scanning speed are adjusted to change the volume energy density, and the AlSi10Mg specimens with different porosities are obtained. The ultrasonic transverse and longitudinal waves were used to test the specimens, and the corresponding sound velocity and attenuation coefficient were obtained. The results show that the transverse and longitudinal sound speeds are inversely proportional to the porosity size, and the attenuation coefficients are directly proportional to the porosity size. When using sound velocity to characterize the porosity, the absolute value of longitudinal sound velocity is more variable, so the accuracy is better. Because the shear modulus of longitudinal sound velocity changes more than that of transverse sound velocity, the linearity is 22% higher than that of transverse sound velocity. When the attenuation coefficient is used to characterize the porosity, the accuracy of transverse wave is better than that of longitudinal wave because transverse wave of the same frequency is shorter in wavelength, and is more sensitive to the direction of polarization, so the linearity is 13% higher than that of the longitudinal wave.