Abstract: According to complex number elastic theories, the solution of attenuation coefficient and phase velocity of EPDM5Si polymer composite materials were expatiated with two kinds of methods (direct contact method and waters delay method). The tangent value of the loss angle, i.e. the ratio of the store energy modules and the loss energy modules was deduced. The result of the tangent value of the loss angle was validated by dynamic mechanical analysis (DMA) method, and proved to be exactitude. An evaluation system for polymer composite material by UT was established.