A SAS system includes an SAS controller, a first expansion card, a second expansion card, and a third expansion card. The first expansion card includes a first port and a second port. The second expansion card and the third expansion card establish a communication connection to the SAS controller by using the first expansion card. The first expansion card establishes a communication connection to the second expansion card through the first port. The first expansion card establishes a communication connection to the third expansion card through the second port. The second expansion card is connected to the third expansion card.