The understanding of biofilm is important for many research and industrial fields since biofilm is omnipresent. Although many studies argue that biofilm is porous, most of the precedent models assume biofilm as impervious materials. Thus, we introduce a biofilm model which consider the porosity of biofilm, and conducted experiments with Pseudomonas aeruginosa (PA) in microfluidic devices. To circumvent the difficulty of computation, we assigned pseudo-viscosity to biofilm. This model is advantageous in that local shear stress can be calculated. Moreover, dynamics over the entire domain may be represented with only one equation which is based on Stokes equation. To test validity of the model, we devised an experimental setup with a syringe pump, a pressure sensor and a microscope to the microfluidic device. This model will be applicable for characterizing the mechanical properties of biofilm in response to flow, which can be utilized for controlling the formation and removal of biofilm.