Carbon microspheres with a uniform size of about 170 μm were prepared in a simple co-flow microfluidic device using solvent extraction method. An ethanol solution of colloidal silica and phenol formaldehyde (PF) resol was used as the dispersion phase, and a mixture of hexane and diisopropylamine was used as the continuous phase. The droplets of PF resol resin/silica were generated in the continuous phase. Colloidal silica assisted the formation of the spherical structure and worked as a pore generator. The continuous phase was also used as extractant and catalyst for PF resin/silica microspheres formation. Curing, drying, carbonization and leaching were used for the post-treatment of the PF resin/silica microspheres to obtain porous carbon microspheres. The carbon microspheres displayed a narrow size distribution and a high surface area of 679 m²/g coupled with adjustable mesopores and large mesopore volume. Carbon microspheres prepared from the dispersion phase with different PF/silica ratios (denoted as carbon/silica (C/Si) ratios) were studied and the formation mechanism of the PF/silica microspheres was deeply explored.