An analytical solution is formulated to predict the deflection of circular piezoactuators for the sake of gas compression in micropumps. The solution is derived from the energy minimization method and Rayleigh–Ritz method based on the Kirchhoff thin plate theory. Energy associated with the micropump includes elastic potential energy of the deflecting actuator, electric potential energy in the piezodiscs and compression work to gas. The proposed analytical solution is validated via the finite element simulations and experimental data. Furthermore, the effects of dimensions and material properties of the piezoactuator on the static pressure rise are discussed; there exist optimal radius ratio of the PZT layer to passive layer, optimal thickness ratio of the PZT layer to passive layer, and optimal ratio of the passive layer thickness to its radius, however, these optimal values are related to pressure load as well. Finally, the static pressure rise and the deflection profile of the piezoactuator have been discussed under the optimal dimensions.