In the blending process of bitumen and SBS, SBS particles gradually swell and form a stable mixture with bitumen because of the following reasons: according to the similarity compatibility principle, the oil content (saturation and aromatic content) in bitumen is compatible with SBS during Brownian motion, and SBS produces swelling. The polarity of the expanded SBS particles is similar to that of the gum in bitumen, and the SBS particles have incomplete compatibility with bitumen. The bitumen with less bitumenene content has better compatibility with the modifier, and the modifier absorbs part of the oil and produces swelling effect. The swelling SBS can improve the pavement performance of the base bitumen. As a result, the SBS particles gradually swell and form a stable mixture with the bitumen. The dynamic balance of bitumen and SBS blending process is achieved by crushing and coalescence process. Under a certain shear stress, the dispersed phase (SBS particles) is broken into smaller particles and coalesced at a certain speed. The smaller the particles in the dispersed phase, the higher the coalescence speed. When the rate of fragmentation and coalescence reaches equilibrium, the state of dispersed phase equilibrium will be reached. This process is a dynamic equilibrium process, through the balance of crushing and coalescence, bitumen and SBS particles can form a stable mixture.