Controlling the size of the droplet generation precisely and constructing an accurate three-dimensional evolution model of droplet structure is essential for the wide application of droplet microfluidic technology. A method to describe the three-dimensional evolution of droplet structure in the breaking regime and steady flow regime in the flow-focusing channel is proposed, and the volume composition mechanism of the droplet is constructed segmented based on the multi-module approach. Based on the four physical quantities of droplet width w, droplet total length L, droplet dip angle "?" and the middle section length of the droplet "?" , a volume calculation model for each module of the droplet was established, and an experimental system was built to verify the model. The results show that in the droplet breakup stage, the relative error of the droplet equivalent radius δ between the predicted model and the experiment ranges from -11% to +17.5%, the average deviation is 3.12 μm. In the steady flow stage, a correction coefficient "?" is introduced to optimize the droplet model. The relative error δ ranges from -15% to +19.7%, and the average deviation is 3.61 μm after the correction. The predicted model takes into account the characteristics of the curved surface of the droplet, which is not only suitable for the squeezing regime, but also satisfies the calculation of the volume of the dripping regime and the injecting regime. The predicted model can accurately predict the interfacial deformation in the droplet generation.