Abstract: A T-shaped microchannel is efficient for monodispersed droplet formation. In order to get a better understanding, the droplet formation process was investigated by numerical simulation and experiment. Silicon oil and precursory sol for hollow glass microspheres were used as the continuous phase and the dispersed phase respectively. A numerical model of the droplet formation was established on the basis of force analysis for a single droplet. Effects of the flow rates on the droplet size were investigated. The results show that the droplet diameters can be controlled by adjusting the flow rates of both phases. Droplet diameters decrease with the increase of continuous phase flow rate at a given dispersed phase flow rate. There is a range beyond which the effect of the continuous phase flow rate becomes weak. The droplet diameters increase with the increase of dispersed phase flow rate. Droplet diameters calculated by the numerical model are close to those by experiment with a deviation around 10%. Based on the simulation and the video, the droplet experiences two phases, namely, the droplet growing under a quasi-steady situation and the stripping. The results help with a better understanding about the droplet formation in a T-shaped microchannel. They also provide good reference for size control of gel microspheres fabricated by sol-microemulsion-gel process.