The invention discloses a brake disc assembly based on an air cooling system, and relates to the technical field of brake discs. The brake disc assembly comprises a boss, two disc bodies are fixedly connected to the circumferential side face of the boss, a circular ring is rotationally connected to the circumferential side face of the boss through a bearing, a plug pin penetrates through the innerwall of an annular cavity, a limiting disc is fixedly connected to the end, located in the annular cavity, of the plug pin, a limiting spring and an expansion air bag are fixedly connected to one side face of the limiting disc, one side face of the expansion air bag is fixedly connected with the inner wall of the annular cavity, and arc-shaped clamping grooves are formed in the two side faces ofthe circular ring. Through the design of the circular ring, the plug pin, the expansion air bag, the arc-shaped clamping grooves, an annular gear and fan blades, the disc bodies and the circular ringrotate differentially, automatic air cooling can be achieved, the heat dissipation effect is good, and the problems that an existing brake disc is poor in heat dissipation effect, the performance of the brake disc can be affected after long-time braking, safety is poor, brake failure is likely to happen, and traffic accidents are caused are solved.