Sublayer fence is one kind of wall shear stress sensors working through measuring the pressure between near-upstream and near-downstream of the fence submerged in the sublayer. So the relationship between wall shear stress and the corresponding pressure is its operational fundamental. However, there is no available mathematic model to describe the wall shear stress - pressure relationship so far. Here a method to establish the model was proposed. The method was then verified through comparing the established model with the experimental data of a developed divice. It showed good match between them in a wide range. A piezoresistive MEMS sublayer fence was designed and fabricated based on the method.