The flow characteristics of EHD induction pumps have been investigated by a numerical method which adds an electric modeling to the conventional CFD. The governing equation for the electric modeling is derived and discretized using the electronic potential as the only dependent variable so that the boundary conditions are satisfied independent of convergence. The numerical results make a good prediction about the frequency-dependent characteristics, which are consistent with both the experiment and the theory. An improvement in understanding the cause of instabilities is achieved to show that the decrement of volumetric force in the local region induces backflow resulting in the instability. The vulnerability was discovered under the conditions of low frequency and large channel depth. The micro-pump has a maximum flow rate at an optimum channel depth due to the flow instability at larger depths and the flow resistance at smaller one have an undesirable influence upon the one-directionality of flows.