A data processing method and apparatus, and a terminal device are described. The method includes: receiving, by a mobility management device, uplink data sent by a terminal device by using a NAS message, and determining, based on a processing capability of the mobility management device, whether the mobility management device is overloaded; and when the mobility management device is overloaded, instructing, by the mobility management device, the terminal device to transmit the uplink data through a user plane. The data processing method and apparatus may improve communication quality, especially when a bearer between the mobility management device and a service device is not set up, the bearer does not need to be first set up and then released, saving signaling and resources.