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In vivo tumors develop in a three-dimensional manner and have unique and complex characteristics. Physico-biochemical barriers on tumors cause drug resistance and limit drug delivery efficiency. Currently, 2D cancer cell monolayer platforms are frequently used to test the efficiency of new drug materials. However, the monolayer platform generally overestimates drug efficiency because of the absence of physico-biochemical barriers. Many literatures indicated that a 3D tumor spheroid model has very similar characteristics to in vivo tumor models, and studies demonstrated the accurate prediction of drug efficiency using this model. The use of a 3D tumor spheroid model in drug development process remains challenging because of the low generation yield and difficulties in size control. In this study, we developed a droplet-based microfluidic system that can generate cancer cells encapsulated by micro-droplets with very high generation yield (16–20 Hz, 1000 droplets/min). The system can control the number of encapsulated cancer cells in the droplet or diameter of the 3D spheroid model precisely between 50 and 150 μm. Moreover, the formed 3D tumor spheroid model can be cultured for >2 weeks by an additional step of droplet disruption and recollection, and can grow up to 245 μm in diameter.The developed droplet based microfluidic system can control the size of 3D tumor spheroid models with very high throughput for the drug test platform.