A method, device, and system for multiplexing and mapping optical signals and demultiplexing and demapping optical signals are provided. The method for multiplexing and mapping optical signals includes the following steps: A label object that indicates a multiplexing and mapping relation is acquired. The label object includes a label and a label header. The label includes a type indication field and a TS indication field. The label object predefines a multiplexing and mapping policy about a first optical signal on a first optical channel and a second optical signal on a second optical channel. The first optical signal is multiplexed and mapped to the second optical signal according to the multiplexing and mapping policy. Therefore, when optical signals are multiplexed and mapped and are demultiplexed and demapped, so that an advantage of saving signaling overhead is realized.