Geometry of single tracks has a significant influence on the forming efficiency, surface accuracy and internal quality of metal additive manufacturing parts. Herein, a 3D numerical model of 7075 aluminum alloy single tracks forming process during liquid metal flow rapid cooling additive manufacturing was established to reveal the effect of thermal behaviors and fluid flow on the geometry of 7075 aluminum alloy single tracks. The 7075 aluminum alloy single tracks with controllable geometries were fabricated by self-developed liquid metal flow rapid cooling additive manufacturing equipment. The results show that the variation of the solidification volume of 7075 aluminum alloy melt in spreading stage and the solidification velocity in accumulation stage results in the variety of the spreading and accumulation kinetic energy of 7075 aluminum alloy melt, which decide the geometry of 7075 aluminum alloy single tracks. The geometry of 7075 aluminum alloy single tracks can be controlled by adjusting the process parameters such as nozzle travel speed and melt temperature, which have a significant effect on the solidification volume and solidification velocity during single tracks forming process of liquid metal flow rapid cooling additive manufacturing.