The fused deposition modeling rapid prototyping system is based on the manufacturing principle of layer by layer. The sprayer is the key component which achieves the fused deposition process. Based on the polymer rheological property, the structure design and theoretical analysis of the mini-plunger sprayer of SW2502 fused deposition modeling system are studied. The plasticizing capacity of the mini-plunger sprayer is analyzed in theoretically. It’s very important for the fused deposition modeling process to maintain a stable plasticizing capacity. The driving force of ABS feed is related to several process parameters such as structure form of sprayer and material property, etc. The barrel and nozzle design should be fit for mobility, purity and mechanical property of ABS feed. The modified ABS feed adopts self-pressure-adding driving method to conquer the pressure losses of barrel and nozzle. The plasticizing capacity of the sprayer is more than 20g/h.