Generating liquid droplets is ideal for many applications including respiratory drug delivery because the droplets have uniform properties and can be easily controlled, sampled, and analyzed. In this study, a micropump-based droplet generator is proposed to produce the liquid droplets of micron to nano size. Numerical simulations were carried out to evaluate the ability of the proposed droplet generator device to produce liquid droplets. The velocity and diameter of the droplets generated by the droplet generator device were calculated, and the performance of the device’s flow rate and power consumption was evaluated. The effects of actuation frequency, actuation modes, and nozzle geometry on the performance of the device were investigated. Results showed that the proposed device can produce micron-/nano-sized liquid droplets with low power and the advantages of the proposed droplet generator device over traditional devices were discussed.