A service data transmission method, comprising: obtaining, by a media access control MAC entity of a first communications device from an upper layer of the first communications device, first data on each of at least one first logical channel and second data on each of at least one second logical channel, wherein a service type or a destination address of the first data is different from a service type or a destination address of the second data; generating, by the first communications device, a MAC protocol data unit, PDU, wherein the MAC PDU comprises the first data obtained on each first logical channel and the second data obtained on each second logical channel, the MAC PDU further comprises a first identifier and a second identifier, the first identifier is used to indicate the service type or the destination address of the first data, and the second identifier is used to indicate the service type or the destination address of the second data, the MAC PDU further comprises a first unit and a second unit, all content of the first unit is located before the second unit, the first unit comprises the first identifier and the first data that is on each first logical channel, and the second unit comprises the second identifier and the second data that is on each second logical channel, and the MAC PDU further comprises a MAC control element, wherein: when the MAC control element is comprised in the first unit, the MAC control element is valid for at least one second communications device corresponding to the first identifier; or when the MAC control element is comprised in the second unit, the MAC control element is valid for at least one third communications device corresponding to the second identifier; or when the MAC control element is not comprised in the first unit and the second unit, the MAC control element is valid for both at least one second communications device and at least one third communications device; or when the MAC control element is not comprised in the first unit and the second unit, the MAC control element is valid for all communications devices that receive the MAC PDU; and sending, by the first communications device, the MAC PDU through a direct link to the at least one second communications device and/or the at least one third communications device. obtaining, by a media access control MAC entity of a first communications device from an upper layer of the first communications device, first data on each of at least one first logical channel and second data on each of at least one second logical channel, wherein a service type or a destination address of the first data is different from a service type or a destination address of the second data; generating, by the first communications device, a MAC protocol data unit, PDU, wherein the MAC PDU comprises the first data obtained on each first logical channel and the second data obtained on each second logical channel, the MAC PDU further comprises a first identifier and a second identifier, the first identifier is used to indicate the service type or the destination address of the first data, and the second identifier is used to indicate the service type or the destination address of the second data, the MAC PDU further comprises a first unit and a second unit, all content of the first unit is located before the second unit, the first unit comprises the first identifier and the first data that is on each first logical channel, and the second unit comprises the second identifier and the second data that is on each second logical channel, and the MAC PDU further comprises a MAC control element, wherein: when the MAC control element is comprised in the first unit, the MAC control element is valid for at least one second communications device corresponding to the first identifier; or when the MAC control element is comprised in the second unit, the MAC control element is valid for at least one third communications device corresponding to the second identifier; or when the MAC control element is not comprised in the first unit and the second unit, the MAC control element is valid for both at least one second communications device and at least one third communications device; or when the MAC control element is not comprised in the first unit and the second unit, the MAC control element is valid for all communications devices that receive the MAC PDU; and sending, by the first communications device, the MAC PDU through a direct link to the at least one second communications device and/or the at least one third communications device. when the MAC control element is comprised in the first unit, the MAC control element is valid for at least one second communications device corresponding to the first identifier; or when the MAC control element is comprised in the second unit, the MAC control element is valid for at least one third communications device corresponding to the second identifier; or when the MAC control element is not comprised in the first unit and the second unit, the MAC control element is valid for both at least one second communications device and at least one third communications device; or when the MAC control element is not comprised in the first unit and the second unit, the MAC control element is valid for all communications devices that receive the MAC PDU; and sending, by the first communications device, the MAC PDU through a direct link to the at least one second communications device and/or the at least one third communications device.