The distribution of shear stress on the bottom of the parallel plate flow chamber under different inlet velocities was analyzed by numerical simulation. In the present experimental study, the projection planes of the relative errors at 0.7% level were obtained, and then the efficient region and the actual entrance length were further corrected by introducing the concept of relative error. The results showed that the efficient region of the chamber increased with the direction of length while the inlet velocity was increased, and the actual entrance length was much greater than that of the theoretical entrance length. Therefore, in accordance to the needed range of shear stress in experiment and to the needed efficient region area, the optimum design of the flow chamber is necessary.