The porosity had a great influence on the properties of the composites. To solve the problem that ultrasound could not well characterize high porosity composite materials,the characteristics and nonlinear characteristics of ultrasonic power spectrum were applied to characterize porosity of high porosity quartz phenolic composites, which is the effect of pores on the attenuation of fundamental amplitude and the breeding of harmonic amplitude in frequency domain. The results show that both methods can effectively characterize the pore content of high porosity composites. It is easy to measure the ultrasonic power spectral characteristic parameters based on the fundamental analysis in frequency domain, and it decreases with the increase of pore, which has some advantages when the porosity is low. The second order nonlinear characteristic parameters of the ultrasonic wave based on harmonic analysis are increasing with the increase of porosity, which is more advantageous to the high porosity characterization.