This research is to numerically investigate the flow analysis of thermopneumatic micropump with three different thicknesses of PDMS membrane in micropump owing to the thermal expansion with uniform heat flux in the PDMS membrane. Velocity, temperature distributions and flow rates over the flow domain with different membrane thicknesses in the micropump are numerically calculated for the performance evaluation of pressure increase in micropump with uniform inlet velocity and temperature. According to the calculations of local maximum velocity at outlet, higher thickness of PDMS membrane(500μm) give larger local velocity in the micropump and maximum local velocity occurred at the center of the micropump with respect to the axial direction.