Abstract: The combination of low-melting-point metal and polymer can not only yield electrically and thermally conductive composites with high performances, but also provides a new model to the investigation of multiphase and multi-ingredient polymer systems. In order to recognize the structure changes of low-melting-point metal liquid/polymer melt composite system under outfield effect systematically, the fibration phenomenon of Sn droplets in liquid Sn/molten polyethylene composite system under tensile condition were studied by optical microscope firstly. Then, the size of Sn particles in Sn/polyethylene composite systems at different tensile degrees was measured and the effect of tensile degree on the size of Sn particles was investigated. Finally, the fibration mechanism of Sn droplets was revealed. The results show that during the tensile process of liquid Sn/molten polyethylene composite system, the greater the Sn droplet diameter is, the earlier begins to fiberize. The diameter of fibrous Sn particles depends on the tensile degree of composite system, and the length depends on the volume of Sn droplet. The obtained conclusions can provide theoretic guidance to the preparation of metal/polymer composite with high performances.