Numerical simulations are performed to explore the fluid physics of droplet ejection process for a full-size piezoelectric inkjet printhead. In the analysis, the theoretical model takes account of a set of three-dimensional transient conservation equations of mass and momentum, with the incorporation of the continuous surface force model for treating the interfacial surface tension effect. The resultant governing equations are solved using an iterative semi-implicit method for pressure-linked equations consistent (SIMPLEC) algorithm for determining the flow properties. The volume-of-fluid (VOF) method in conjunction with the multi-dimensional piecewise linear interface construction (PLIC) technique is applied to characterize the behavior of liquid surface movement. Using the design configuration of a test piezo-diaphragm printhead, the time evolution of the gas-liquid interface is calculated for a complete ejection cycle of 164 μs. The flow and transport phenomena in various stages, including the ink filling, ejection, and droplet formation, are thoroughly examined in this work.