Using composite materials to replace aluminum alloy, steel or titanium alloy is of far-reaching significance. With the development of new material science, the advantages of direct extrusion fabrication are becoming increasingly prominent. In principle, direct extrusion fabrication is suitable for any paste or gel composite material with or without additives. The purpose of this study is to find out the general rheological parameters of thermosetting epoxy resin in the direct extrusion fabrication application by discussing the rheological properties and extrusion fabrication properties of the composite. The rheological behavior of the composite was designed by adding thickener. A gantry pneumatic extrusion 3D printer was designed and built to test and analyze the printing effect of composite materials. Combined with the experimental results, the influence of nozzle height on printing results was analyzed, and a calculation method suitable for critical value of nozzle height was proposed. The effects of shear rate, extrusion rate and extrusion pressure on the molding quality of materials were also analyzed. Aiming at the problem of multi-layer printing, a method for calculating the critical value of nozzle height of multi-layer printing was proposed. The above conclusions provide guidance methods for the extrusion 3D printing of composite materials.