Among the various methods of additive manufacturing, FDM has developed due to the availability, simplicity and cheapness of the equipment. However, due to the fact that the material used in this process are mostly thermoplastic, they often do not offer good mechanical properties compared to other additive manufacturing methods, and this limits the use of FDM for rapid proyotyping and non-industrial applications. So, the idea of ??using composites instead of neat polymer is proposed. To end this, continuous reinforcing fibers are added to the molten polymeric material inside of the head during processing and then extrusion is performed. Obtaining this goal, the design of the head was modified based on the above mentioned concept. In this regard, first the design of the heatsink and then its analysis was done in commercial multiphysics COMSOL software. In these analysis, the parameters are obtained in such a way that in addition to satisfy the desired requirments of the head, it fits to the available heater and solves the issue. Then, rheological analysis of the flow is performed by applying the boundary conditions obtained from thermal analysis. This analysis is performed to ensure the proper condition of the inlet filament and guarantees no damage to the components and injection needles. After designing, manufacturing and achieving proper performance of the head, compound ABS polymer and fiber glass materials are injected into the head and extruded throuth the nozzle of the equipment. The experimental result show the increase of strength by 248%. This results prove the improvement of mechanical properties of composite fiber produced by this new device. Key words: 3D printer, continues fiber reinforced composites, Additive manufacturing