This study focuses on the development of a 3D printing extrusion module using high-density polyethylene (HDPE) pellets. HDPE pellets were selected instead of filament-based materials with the aim to reduce costs and improve efficiency. The primary objective of this study was to develop an extrusion module that improves extrusion quality and achieves consistent, high-quality layering by monitoring the melting and extrusion temperatures and pressures of HDPE pellets throughout the extrusion process. The extrusion nozzle structure was improved by applying appropriate pressure during extrusion. To improve adhesion to the substrate and interlayer bonding, the substrate was preheated with hot air, thereby improving the overall performance of the additive manufacturing process. Experimental results showed that the temperature could be controlled within 10% of the target 210 °C, effectively melting the HDPE pellets. In addition, applying pressure in accordance with the set values resulted in uniform material flow and improved bonding strength. In conclusion, the development of an HDPE 3D printing extrusion module capable of monitoring the temperature and pressure is expected to improve the efficiency and quality of the additive manufacturing process, resulting in improved layering quality.