This study presents a diffuser micropump and characterizes its output flow rates, like the parabola shape on the frequency domain and the effecting factors. First, equivalent circuit using fluid-electric analogy was built up; then, the flow rate analysis results were compared to experiment results to verify the applicability of the circuit simulation. The operation frequency was 800 Hz for both cases and the maximum flow rates were 0,078 and 0,075 μ1/s for simulation and experiment result, respectively. The maximum flow rate difference was 3.7%. The circuit then was used to analyze the inertial effects of transferred fluid as well as system components to the output flow rates. This work also explains why the flow rate spectrum has the shape of parabola. The analysis results showed that without inertial effects, the micropump flow rates are linearly proportional to the operation frequency; otherwise it has parabola shape. The natural frequency of the actuatormembrane structure was recognized using finite element method to verify if this parameter affects the characteristics of the flow rates. The experiment and simulation results demonstrated 800 Hz and 91.4 kHz for the frequency of the maximum pumping flow rate and the first mode natural frequency of actuator-membrane structure, respectively. It indicates that the structure natural frequencies of the actuatormembrane structure do not play any role to operate the micropumps.