A coaxial injector is mainly used in large-scale liquid rocket engines. By utilizing optical methods, this research studies the effects of the gas to liquid velocity ratio (2.9-60), gas layer thickness (1.2-2.4 mm), and liquid physical properties (surface tension and viscosity) on the breakup and atomization of coaxial liquid jet spray. The spray angles, droplet size distributions, and breakup processes at different experimental conditions are observed and analyzed. The results reveal the significance of the breakup of the coaxial jet spray as the surrounding high-speed air confines the spray spatially and forces the inherent unstable liquid column into spiral-type turning, then elongates into a ligament before instantaneous breakup. Once the liquid jet has broken up, the outer high-speed air appears to have no further effect on the spray. Owing to this controlling breakup process, the spray angle appears to be increased with increasing velocity ratio and decreased with increasing gas layer thickness, and the droplet size distribution of coaxial jet spray appears to be uniform, concentrated, and invariant after the jet has broken up. Liquid viscosity shows a strong effect on coaxial jet spray. With higher viscosity, the liquid ligament is stretched wider before disintegration; that is, the liquid ligament may utilize more energy of the surrounding high-speed air for liquid atomization, thus producing a larger spray angle and smaller droplet sizes, as observed in the experiments.