A theoretical study with non-Newtonian fluid model was conducted on the per formance of the Maddock mixing head(MMH) in plasticating single-screw extrusion. In this study, the flow analysis network(FAN) method with the corresponding viscosity, so called, the equivalent non-Newtonian viscosity was used for the prediction of pressure variation in both the down-channel and cross-channel direction of MMH. And for the experimental study, the published data were used. Two kinds of screws with the MMH were used, namely:one screw (exp.# 28 similar to 36) to measure the pressure difference between the entrance and the exit of the mixing head in the down-channel direction and the other screw (exp.# 40 similar to 49) to measure pressure variations in the cross-channel direction in the middle of the mixing head. In this study we tried it by using the parameter h(1). The equivalent non-Newtonian viscosity of power law model with drag now was used to simulate the experimental results. This study made the progress on the agreements between experimental results and theoretical predictions.