The purpose of this study is to investigate fuel droplet dispersion and mixture formation in a practical twin-fluid atomizer for a practical oil furnace of 1 MW. In this experiment, droplet size, velocity and dispersion data were measured to show two-dimensional droplet velocity vectors using phase Doppler technique (PDA/PDPA). Fuel droplet dynamics and spray characteristics are discussed by two-dimensional size-classified droplet vector and their slip velocities vector. The spray dynamics is investigated by not only Sauter mean diameter but also each size-classified velocity. The results showed that the size classified technique was suitable and the strong penetration of small droplet near nozzle and the much entrainment flow were yielded at the middle of the jet plane. The injection pressure was varied to show the spray characteristics changes for different conditions.