Swirl injectors are widely used in aerospace propulsion systems because they exhibit high mixing and combustion efficiencies of the propellant. Unlike a single liquid injector, a coaxial gas-liquid swirl injector, in which droplet breakup is accelerated by the gas flow, depends on the droplet generation mechanism at the beginning of the mixing process. High-velocity gas flows affect droplets and can atomize them into fine droplets. This can allow the gas swirl injector to have a more direct effect on the liquid film. In this study, two types of gas-liquid coaxial swirl injectors were used in the experiments. The droplet distribution and the formation mechanism of the fine droplets were investigated through the analysis and comparison of the longitudinal-sectional shape of the spray according to the supply conditions of the internal and external mixing injectors. A high-performance laser was used to facilitate the measurement of the vertical sections of the spray, and multiple scattering signals were removed from the image using the double pulse structured laser illumination planar imaging method.