Abstract: The objective of this paper is to review and assess various models, experiment techniques and numerical methods for the analysis of the fluid mechanism about the tip gap leakage flow within turbomachines. The origins and effects of tip gap leakage flow on the performance of turbomachines are discussed with the emphasis on the physical origins of tip gap leakage flow. Blades are concerned with two types of flows, that is diffusing, or compressor type flows and accelerating, or turbine type flows. A brief review on the tip gap leakage flow of the blades is made as a main content of the paper. It can be found from the review that the major issues at present about the tip leakage flow of turbomachinery are focused on the leakage vortex structure, the leakage flow model, the vorticity, and the shock-leakage vortex interaction, etc. Meanwhile, recommendations are made for future research, including the vorticity in high-speed turbine and compressor, the tip leakage vortex breakdown, the relationship between stall and leakage flow, and the size of blockage region.