The needle-free injection is a new technique for treating subcutaneous drug delivery through penetrating the skin with a high-speed liquid drug jet. The present study aims to reveal fluid dynamics characteristics of the needle-free injection. The operational parameters such as the driving pressure, the nozzle diameter and the liquid volume were investigated for an air-powered needle-free injection system using experimental techniques. The results show that the peak stagnation pressure determines the penetration performance of the jet and is significantly affected by the driving pressure, nozzle diameter and liquid volume. Furthermore, the entire injection process of fluid in the gel can be defined as two phases of penetration and diffusion. Thus, the dispersion characteristics of fluid in different phases could be controlled by an effective combination of the nozzle diameter and liquid volume. Overall, the obtained conclusions provide a sound support for understanding the operation of the needle-free injector.