The thermal effect of MEMS wall shear stress sensors is analyzed by using the computational fluid dynamics（CFD） commercial software FLUENT.The simulating results demonstrate that it is very necessary to add a vacuum cavity or an air cavity beneath the hot-film of MEMS wall shear stress sensors.The result of calculation in flowing water shows that the difference between the effects of the vacuum cavity and the air cavity is very small in the temperature distribution and the heat transfer rate to the flowing water

and the vacuum cavity can signally reduce the heat lost irretrievably to the substrate

which is very necessary to improve the sensitivity of wall shear stress sensors.In additional

the geometry of sensors also influence the heat transfer rate of wall shear stress sensors.