To make the acousto-ultrasonic measurements more accurate and reproducible, a new method is developed for the measurement of stress wave factor (SWF) of acousto-ultrasonic technique. The energy content of the received signal is used to rank the materials interaction with the propagating stress wave. And the energy content parameter is used for better estimation of the signal instead of ring down counts. The effects of gain, threshold voltage, area, amplitude and RMS value on SWF of unfilled and filled with mica/graphite glass fibre reinforced epoxy resin composites are studied using modified AU technique of stress wave factor. Finally, flexural and tensile strength of these hybrid composites are predicted for the relation with the stress wave factor. The results show that the modified acousto-ultrasonic of stress wave factor can evaluate with greater accuracy than the conventional SWF method. The stress wave signal analysis shows that a good correlation exists between RMS values, area and maximum amplitude of the wave signal and stress wave factor of hybrid composites.