Three-dimensional (3D) tumor spheroids offer unprecedented capability for drug screening because of their unique features such as spatial 3D structure, relevant physiological responses, more complex intercellular network, and stroma-cancer cell interactions. Microfluidic technology provides a facile strategy to make uniform tumor spheroids with potential of high-throughput production. In this article, we develop a microfluidic approach to produce core-shell alginate particles, which allows the separate confinement of different cells in the core and shell structure. To reconstitute the complex tumor structure, we encapsulated tumor cells in the core and stromal fibroblast cells in the shell. These coculture tumor spheroids were applied for drug evaluation showing similar drug resistance as those prepared using conventional methods in well plates. These results demonstrated that our microfluidic approach are facile and versatile for making various tumor spheroids with uniform size but different components to better mimic tumor microenvironment. Moreover, the production rate of around 200 spheroids/min indicates the great potential of this approach for high-throughput drug screening.