A data transmission method, comprising: receiving, by a first network device, first indication information from a second network device, wherein the first indication information indicating that a terminal device is successfully handed over from a third network device to the first network device or that the third network device has released a context of the terminal device; and detecting, by the first network device, a mobility problem based on the first indication information; characterized in that the method further comprises: receiving, by the first network device, second indication information from the second network device, wherein the second indication information indicating a radio link failure between the terminal device and the first network device; and the detecting, by the first network device, a mobility problem based on the first indication information comprises: if duration between a moment at which the first network device receives the second indication information and a moment at which the first network device receives the first indication information falls within a first preset threshold, determining, by the first network device, that secondary network device change of the terminal device is toc early, thereby third indication information indicating that secondary network device change of the terminal device is too early is to be sent by the first network device to the second network device. receiving, by a first network device, first indication information from a second network device, wherein the first indication information indicating that a terminal device is successfully handed over from a third network device to the first network device or that the third network device has released a context of the terminal device; and detecting, by the first network device, a mobility problem based on the first indication information; characterized in that the method further comprises: receiving, by the first network device, second indication information from the second network device, wherein the second indication information indicating a radio link failure between the terminal device and the first network device; and the detecting, by the first network device, a mobility problem based on the first indication information comprises: if duration between a moment at which the first network device receives the second indication information and a moment at which the first network device receives the first indication information falls within a first preset threshold, determining, by the first network device, that secondary network device change of the terminal device is toc early, thereby third indication information indicating that secondary network device change of the terminal device is too early is to be sent by the first network device to the second network device. receiving, by the first network device, second indication information from the second network device, wherein the second indication information indicating a radio link failure between the terminal device and the first network device; and the detecting, by the first network device, a mobility problem based on the first indication information comprises: if duration between a moment at which the first network device receives the second indication information and a moment at which the first network device receives the first indication information falls within a first preset threshold, determining, by the first network device, that secondary network device change of the terminal device is toc early, thereby third indication information indicating that secondary network device change of the terminal device is too early is to be sent by the first network device to the second network device.