Abstract: The ultrasonic signal processing and analysis system which is based on the VC++ software had been established. For the characterization and evaluation of materials, the acquisition, processing, calculation and so on of ultrasonic signals were integrated in the system. It not only could finish the regular processing of signals, but also could carry out calculation, extraction and analysis of multi-type characteristic parameters. To extract Energy for limited trequency band(ELFB)and energy for principle frequency(EPF), the ultrasonic signals tested with Carbon fiber reinforced polymer(CFRP) had been processed and analyzed. Numerical fitting was prosecuted to establish the relationship between ELFB, EPF and CFRP porosity. The phenomenon of critical porosity existed on the fitted lines. The research provided a potential approach for testing the porosity of CFRP.