This application provides a data communications system and method. The system includes a first chassis and a second chassis. The first chassis includes a first high-performance switching module and a first low-performance switching module. The second chassis includes a second high-performance switching module and a second low-performance switching module. The first high-performance switching module is connected to the second low-performance switching module. The first low-performance switching module is connected to the second high-performance switching module. The first high-performance switching module is configured to connect to a third low-performance switching module in a third chassis that is to be added to the communications system. The second high-performance switching module is configured to connect to a fourth low-performance switching module in the third chassis that is to be added to the communications system. Removal of a central switching chassis reduces a footprint of the data communications system and lowers power consumption and costs. During capacity expansion, there is no need to change cables between deployed chassis. Therefore, the capacity expansion is convenient, and smooth capacity expansion is implemented.