A service data transmission method, comprising: receiving, by a mobility management entity, a request message, wherein the request message comprises transmission mode indication information, and the transmission mode indication information is used to indicate that a terminal transmits service data by using a non-access stratum, NAS, signaling message; determining, by the mobility management entity, second service authorization information of the terminal based on subscription information of the terminal in response to the mobility management entity determines, based on the request message, that the terminal transmits the service data by using the NAS signaling message, wherein the second service authorization information comprises information used to indicate a service type and a first priority that is allowed to be used by the terminal to transmit the service data; and sending, by the mobility management entity, the second service authorization information to the terminal, wherein the second service authorization information further comprises second quota information, and the second quota information is used to indicate a volume of service data that is of a second priority which is higher than the first priority and that is allowed to be sent within a particular time, such that when the terminal determines that a volume of sent service data of the second priority does not reach the second quota information, the terminal sends the service data at the second priority, and when the terminal determines that a volume of sent service data of the second priority reaches the second quota information, the terminal sends the service data at the first priority. receiving, by a mobility management entity, a request message, wherein the request message comprises transmission mode indication information, and the transmission mode indication information is used to indicate that a terminal transmits service data by using a non-access stratum, NAS, signaling message; determining, by the mobility management entity, second service authorization information of the terminal based on subscription information of the terminal in response to the mobility management entity determines, based on the request message, that the terminal transmits the service data by using the NAS signaling message, wherein the second service authorization information comprises information used to indicate a service type and a first priority that is allowed to be used by the terminal to transmit the service data; and sending, by the mobility management entity, the second service authorization information to the terminal, wherein the second service authorization information further comprises second quota information, and the second quota information is used to indicate a volume of service data that is of a second priority which is higher than the first priority and that is allowed to be sent within a particular time, such that when the terminal determines that a volume of sent service data of the second priority does not reach the second quota information, the terminal sends the service data at the second priority, and when the terminal determines that a volume of sent service data of the second priority reaches the second quota information, the terminal sends the service data at the first priority.