The tackifying modification of polyethylene terephthalate( PET ) was with epoxy resin as chain extender, and the rheological property were studied, the effects of the types and content of chain extender on the rheological properties of composite materials under different technology conditions were investigated. The results show that PET is pseudoplastic fluid before and after tackifying modification, E20 can greatly increase the apparent viscosity of the melt among E20, E22, E23 3 kinds of epoxy resin.In the experimental study, the apparent viscosity of PET melt and flow activation energy increase with the increase of the content of epoxy resin, the apparent viscosity of the melt decreases as the temperature rises. Under low shear stress, the viscosity flow activation energy of the melt is higher, the change of the apparent viscosity to temperature is more sensitive, and at high shear stress, the viscosity flow activation energy of melt decreases, the change of the apparent viscosity to temperature isn’t sensitive.