In wood/plastic composite of high wood filler content, filler dispersion in resin is important which determines mobility of compound and mechanical properties of products. This work reports on the dispersion of components in compound by evaluation of viscoelasticity using a cone rheometer. The effects of size of cellulose fiber and resin content on viscoelasticity were analyzed, and the dispersion of cellulose is discussed to reach the following conclusions: The viscoelasticity measured by a cone rheometer was dependent on the dispersion state of compound, and evaluation of viscoelasticity affords the evidence for dispersion state of filler in compound; On the basis of viscoelastic evaluation of compound with different resin content, a model for dispersion of cellulose and resin with tangle of fiber is proposed; Viscoelastic analysis showed that cellulose size has influence on tangle of fiber, and results of viscoelasticity and mechanical properties of mold products suggested that an important factor determining tangle of fiber is its average aspect ratio. The proposed analysis of viscoelasticity presents a new technique for estimating the dispersion state of compound of high filler content which is hardly accessible by conventional fluid evaluation methods. The present method is simple and useful for quality control in manufacture.