To precisely control the size of droplets produced in a flow-focusing microdroplet generator, the pressure-driven device is designed to control the flow rates of the fluids during the experiments of droplet generation. While monodisperse droplets are produced by the pressure-driven microfluidic flows, the nonlinear relation between the droplet length and the driving-pressure ratio of the two phases can be observed for the open-loop control of droplet generation. In particular, by using the method of the closed-loop control of droplet generation, good agreements are shown between the tested size of droplets and the predicted droplet size. Consequently, based on the closed-loop control of droplet generation under pressure-driven flows, the effects of the nonlinearity of the flow-focusing microchannel on the control accuracy of the droplet size is drastically reduced, which can significantly increase the control precision of the droplet size in the flow-focusing micro droplet generator. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.