An interconnection system, an apparatus, and a data transmission method. In the interconnection system, to-be-transmitted data is converted into a data packet in an optical signal form for transmission, and a control packet corresponding to the data packet is transmitted in an electrical signal form and includes routing information of the data packet. When the control packet passes through a switching node, the switching node directly determines, according to the routing information in the control packet, a neighboring node that serves as a next hop, and opens, in the switching node, an optical path used to transmit the data packet. Because no optical-to-electrical or electrical-to-optical conversion needs to be performed on the control packet and the data packet during an entire transmission procedure, problems of an extra delay and power consumption caused by electrical-optical-electrical conversion can be reduced, thereby improving data transmission efficiency.