Abstract: The goal of this paper is to study the short fiber reinforced composite used for manufacturing parts by the RPM (Rapid Prototyping/Part Manufacturing) process. In the experiment, the short glass fiber reinforced ABS composite is modified by adding a series of agents. The toughness and mechanical properties of the resultant composite filament from injection molding machine are improved so as to be used for FDM (Fused Deposition Manufacturing) process. The effect of the modification is evaluated from microcosmic aspect. The samples are made by modified short fiber reinforced ABS in the RPM equipment, and then the effect of the modification is analyzed.