Abstract: The rheological properties of PVC/M-80 blends was studied with a high pressure capillary rheometer and HAKKE torque rheometer. The effects of the content of the M-80 and processing conditions on the rheological properties of PVC/M-80 were investigated. The results show PVC/M-80 melt blends system is a typical non Newtonian pseudoplastic fluid; the balance torque and melt temperature decrease with the increase of the content of M-80, the balance torque linearly reduces with the increase of the processing temperature, but the effect of rotor speed on rheological properties is not obvious in conventional processing range.