Dynamic rheological behavior was measured with rotational rheometer for two kinds of polypropylene(PP)/high density polyethylene(HDPE)/ethylene-propylene-diene-terpolymer rubber (EPDM) ternary blends( PP EPS 30RA/HDPE 8916/EPDM and PP T30S/HDPE 5306/EPDM), and the loss moduli(G″)-frequency(ω) data was fitted by the generalized Maxwell model. The results show at low ω, the complex viscosity of the two blends increases gradually with increase of PP/HDPE mass ratio, but the storage modulus first increases then drops, the maximum value arrived at PP/HDPE mass ratio of 70/30. When the mass ratio of EPS 30RA/HDPE 8916/EPDM is 30/70/3, 50/50/3 and 70/30/3, G″ at low ω reveals secondary plateau, while G″ of PP T30S/HDPE 5306/EPDM blends does not. When the mass ratio of PP/HDPE/EPDM is more than 50/50/3,the characteristic relaxation time of the two blends increases gradually. The relaxation modulus -relaxation time curves of the two blends present a shape of besom, the relaxation time gathered at high modulus, and diverged at low modulus.