Abstract: The capacitive sensor with a micro floating element can measure the wall shear stress in the flow boundary layer directly. The sensor output voltage is linear to the applied wall shear stress and it is much more precise than conventional methods. We built up the analytical model for the sensor design by studying how structural parameters influence the sensor performances. The sensor consists of a floating element, folded tethers, movable comb fingers, fixed comb fingers and anchors, etc. And the sensor performances include measurement range, natural frequency, nonlinearity, sensitivity and resolution. The relationships between structural parameters and sensor performances are clarified explicitly by the analytical model. And the micro-sensor design becomes much easier and more efficient. Static and dynamic calibration were carried out and the results indicate a good agreement with predictions of the analytical model.