Abstract: The vortex generated inside deep grooves obstructs the flow when the gas flows through the clearance on step-deep grooved surfaces. This leads to the decreasing of the leakage rate called the throttling effect as a result. In order to investigate the throttling effect of the rectangular deep grooved surfaces with laminar flow under low Reynolds number, an experimental study on gas hydrostatic lubrication was carried out to compare the flux between the grooved surface and the smooth one. Experimental results show that there was significant throttling effect on deep grooved surfaces, which was enhanced with the increasing Reynolds number. There is also throttling effect under laminar flow which was unstable but kept constant under turbulent flow. The throttling effect depended on structural parameters of deep grooves (e.g. the clearance and grooved depth).