In order to improve the mechanical properties of the poly(trimethylene terephthalate) (PTT), both maleinized acrylonitrile-butadiene-styrene (ABS) and short carbon fiber (SCF) were melt-blended with PTT to prepare the composites and their morphology and properties were investigated in detail. When ABS content is fixed at 5 wt.% in composites, SCF can significantly improve the tensile and flexural strength as well as the impact strength of the matrix. The SCF has good interface adherence with the matrix. At glassy state, the storage modulus increases much with increasing SCF content. At rubbery state, the composites have larger cold-crystallization rate. At molten state, SCF first serves as lubricants and then as viscosity reinforcing agent for the matrix with increasing SCF. The composites melt exhibits increasing elastic behaviors with SCF. The composites have larger crystallization rate, but this accelerating effect decreases with excessive SCF content. The crystals formed in different composites are quite different in size or perfection.