This study investigated the effects of raw fiber materials, fiber content, and coupling agent (CA) content on mixing torque, rheological properties, and crystallization behavior of wood plastic composites (WPC). WPCs were prepared through melt molding processes. This study adopted a response surface strategy of 20 run optimal design for three factors including wood fiber type, fiber content, and CA content. Wood fiber type or wood fiber characteristics influence equilibrium torque and viscosity. The power index n for viscosity as a function of frequency was affected not only by wood fiber content, but also by CA content and wood fiber type. Addition of wood fibers to the system as nucleating agents favors polyethylene crystallization. The values of crystallization enthalpy and melt enthalpy were correlated with wood fiber content and CA content, but they were not affected by wood fiber type. The melt temperatures of polyethylene and composites were comparable. This indicates that the crystallite structure and lamellar thickness are similar.