A service transmission method, comprising: • mapping, by a first transmission device, n client signals with a rate of t to ms/t load subareas of m lanes of FlexO frames, wherein each client signal is mapped to one load subarea, a payload area of each of the m lanes of FlexO frames is divided into s/t load subareas, and each lane of FlexO frame is transmitted by using a FlexO lane with a transmission rate of s, wherein s, t, m, and s/t are all positive integers; • configuring, by the first transmission device, FlexO type information, timeslot overhead information, and signal mapping information for each lane of FlexO frame, wherein the FlexO type information is used to indicate a FlexO group interface type, and the FlexO group interface type indicates the transmission rate of the FlexO lane for transmitting each lane of FlexO frame and indicates that the payload area of each lane of FlexO frame is divided into the s/t load subareas; the timeslot overhead information is used to indicate client signals mapped to the s/t load subareas of each lane of FlexO frame; and the signal mapping information is used to indicate distribution, in each load subarea, of a client signal carried in each of the s/t load subareas of each lane of FlexO frame; and • transmitting, by the first transmission device, the m lanes of FlexO frames to a second transmission device by using m FlexO lanes with the transmission rate of s, characterized in that before the transmitting, by the first transmission device, the m lanes of FlexO frames to the second transmission device by using m FlexO lanes with the transmission rate of s, the method further comprises: configuring, by the first transmission device, quantity overhead information for each lane of the FlexO frame, wherein the quantity overhead information is used to indicate a quantity of load subareas that are in the load subareas of each lane of the FlexO frame and to which client signals are mapped. • mapping, by a first transmission device, n client signals with a rate of t to ms/t load subareas of m lanes of FlexO frames, wherein each client signal is mapped to one load subarea, a payload area of each of the m lanes of FlexO frames is divided into s/t load subareas, and each lane of FlexO frame is transmitted by using a FlexO lane with a transmission rate of s, wherein s, t, m, and s/t are all positive integers; • configuring, by the first transmission device, FlexO type information, timeslot overhead information, and signal mapping information for each lane of FlexO frame, wherein the FlexO type information is used to indicate a FlexO group interface type, and the FlexO group interface type indicates the transmission rate of the FlexO lane for transmitting each lane of FlexO frame and indicates that the payload area of each lane of FlexO frame is divided into the s/t load subareas; the timeslot overhead information is used to indicate client signals mapped to the s/t load subareas of each lane of FlexO frame; and the signal mapping information is used to indicate distribution, in each load subarea, of a client signal carried in each of the s/t load subareas of each lane of FlexO frame; and • transmitting, by the first transmission device, the m lanes of FlexO frames to a second transmission device by using m FlexO lanes with the transmission rate of s, before the transmitting, by the first transmission device, the m lanes of FlexO frames to the second transmission device by using m FlexO lanes with the transmission rate of s, the method further comprises: configuring, by the first transmission device, quantity overhead information for each lane of the FlexO frame, wherein the quantity overhead information is used to indicate a quantity of load subareas that are in the load subareas of each lane of the FlexO frame and to which client signals are mapped.