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. During capacity expansion, there is no need to change cables between deployed chassis.