Abstract: Highly filled wood-plastic composites have better low carbon and environmental protection and market competition advantages. Investigating their rheological behavior during the melting process is of significant importance for optimizing production equipment and improving production efficiency. In this study, the rheological properties of highly filled wood flour/polypropylene composites (HFWFPP) under continuous deformation were analyzed by a homemade compression testing system. The morphological changes of HFWFPP during compression were recorded and analyzed, and the test data were combined with the plug flow model to explore its rheological behavior. The results show that the compression test effectively induced a large-scale uniform flow of the specimens, creating a prerequisite for the accurate expression of rheological behavior. The stresses of the specimen were calculated and analyzed based on the plug flow model, validating the applicability of the model to the compression rheology of HFWFPP and elucidating its compression rheological behavior. Based on this, the influence of wood flour content, initial radius, and coupling agent on the rheological properties of the specimen was quantified. This study provides an effective rheological analysis method for highly filled wood-plastic composites and offers theoretical insights for their production and application.