Measurement of wall shear stress (WSS) has important significance in many fields, such as spacecraft surface flow visualization and drag reduction of solid-liquid interface. Various measuring methods have been developed with the rapid development of micro and nano technology. This paper focuses on the measurement of WSS by using nematic liquid crystal coating. A quantitative model is built to describe the relationship between the variations of director orientation and the WSS based on the curvature elasticity theory of liquid crystal. Then an experiment setup is built to verify this model using 5 CB and 7 CB through the optical method. There is good consistence between the theoretical model and experiment results. Finally, the WSS measuring limits and influencing factors are discussed such as the thickness of the liquid crystal layer, the elastic coefficient of the molecule and measurement resolution.