A data processing method, comprising: receiving, by a mobility management device (103, 403), uplink data sent by a terminal device (101, 401) by using a Non-Access Stratum, NAS, message, and determining, based on a processing capability of the mobility management device (103, 403), whether the mobility management device (103, 403) is overloaded; and when the mobility management device (103, 403) is overloaded, instructing, by the mobility management device (103, 403), the terminal device (101, 401) to transmit the uplink data through a user plane; the method is characterized by further comprising: if the mobility management device (103, 403) has set up a user plane bearer with a service device (104, 404) and the mobility management device(103, 403) has received downlink data from the service device (104, 404), sending, by the mobility management device (103, 403), a back-off timer and downlink data that is not sent when the mobility management device (103, 403) is overloaded, to the terminal device (101, 401) by using the NAS message; wherein the sending, by the mobility management device (103, 403), a back-off timer and downlink data that is not sent when the mobility management device (103, 403) is overloaded, to the terminal device (101, 401) by using the NAS message specifically comprises: carrying, by the mobility management device (103, 403) by using the NAS message, the back-off timer and the downlink data, and sending the back-off timer and the downlink data to an access network device (102, 402), wherein the back-off timer and the downlink data are then sent by the access network device (102, 402) to the terminal device (101, 401) through an Radio Resource Control, RRC, downlink message. receiving, by a mobility management device (103, 403), uplink data sent by a terminal device (101, 401) by using a Non-Access Stratum, NAS, message, and determining, based on a processing capability of the mobility management device (103, 403), whether the mobility management device (103, 403) is overloaded; and when the mobility management device (103, 403) is overloaded, instructing, by the mobility management device (103, 403), the terminal device (101, 401) to transmit the uplink data through a user plane; the method is characterized by further comprising: if the mobility management device (103, 403) has set up a user plane bearer with a service device (104, 404) and the mobility management device(103, 403) has received downlink data from the service device (104, 404), sending, by the mobility management device (103, 403), a back-off timer and downlink data that is not sent when the mobility management device (103, 403) is overloaded, to the terminal device (101, 401) by using the NAS message; wherein the sending, by the mobility management device (103, 403), a back-off timer and downlink data that is not sent when the mobility management device (103, 403) is overloaded, to the terminal device (101, 401) by using the NAS message specifically comprises: carrying, by the mobility management device (103, 403) by using the NAS message, the back-off timer and the downlink data, and sending the back-off timer and the downlink data to an access network device (102, 402), wherein the back-off timer and the downlink data are then sent by the access network device (102, 402) to the terminal device (101, 401) through an Radio Resource Control, RRC, downlink message.