Droplet microfluidics provide an advanced platform for functional material synthesis. However, the process has been largely limited to the scale of laboratory study with the device known as lab-on-chip. Here, a multi-dimensional scale-up strategy based on modularised microfluidic reactors is presented to develop large-scale devices defined as factory-on-chip, achieving throughput enhancement to the industrial production scale. Under the guidance of the derived principle, an up-scaling system is demonstrated with eight microchannels parallelized to form an array, ten arrays stacked as the module, and five modules integrated in a system with 400 channels in total. Experiments showed that the circular array arrangement improved the uniformity of product droplets by 42.4% compared to that achieved with a parallel array. The stacking effect was also investigated with two types of material production systems. Chitosan/TiO2 composite microspheres, as advanced wastewater treatment material, were continuously synthesized in mass production with a narrow size distribution of 3.59%, which could hardly be achieved with conventional methods. The material exhibited a methyl-orange dye removal efficiency of 65.3%, which constitutes an improvement of 10.8% compared to single-component chitosan microspheres.