Abstract: In order to improve the processing flow performance of wood plastic composites (WPC), the capillary rheological properties of the wood flour/high density polyethylene (HDPE) composites modified by ionomer were studied by using a HAAKE Minilab rheometer. Results show that the wood flour/HDPE melts are all pesudoplastic fluid with or without ionomer, which all show the shear thinning effects. Both the shear stress and apparent viscosity of wood flour/HDPE modified by ionomer show the decline trends with the increasing of sodium ionomer and shear rate, which indicates the addition of sodium ionomer could improve the flowability of HDPE melts obviously. The shear stress and apparent viscosity of wood flour/HDPE adding 4wt% sodium ionomer and 4wt% zinc ionomer are both lower than those of the wood flour/HDPE composites adding 4wt% coupling agent maleic anhydride grafted polyethylene (MAH-g-PE), which demonstrates ionomer could improve the flowability of WPC melt much more compared with MAH-g-PE, and decrease the frictional resistance between HDPE and wood flour as melt flows. SEM analysis shows that HDPE polymer has a good coated effect on wood flour after being added ionomer without clear gap between wood flour and HDPE matrix. In addition, there exists a large number of fibrils on the fracture surface of WPC.