This review discusses the studies on fluid dynamics passing through in a high-pressure homogenizer in a narrow gap. In industries, such as fine chemical, biotechnology, food and dairy industry, high-pressure homogenization is used to create a stable emulsion in sub-micron or nano drop size. During the homogenization process, high energy input with extreme shear force have to be applied to reduce the droplet sizes for rough or loosely texture emulsion from the smaller scale to a range of nano scale. This process will then can overcome the Laplace pressure. Laplace pressure is the difference in pressure in between the outside and inside of a curving surface. This pressure (100–500 MPa) will then be converted to dynamic energy, therefore prompting a separation of the coarse emulsion into a smaller droplet. Fluid dynamics involved through the homogenising valve is very complicated. In the homogenizer valve, flow conditions expose to intense changes of energy as the fluid goes to low pressure and high speed from high pressure and low speed. To understand these changes, a computational fluid dynamics (CFD) approach is needed. The objectives of this review are the investigation of a dynamic model for describing the dynamics of drop size distributions and the flow pattern in a high-pressure homogenizer. The effect of drop coalescence in droplets is not included because it relies upon the relative rates of drop collision and surfactant adsorption.