A data transmission method and a device are provided. When determining that the first network element and the second network element is disconnected, the first network element stores identification information of the last frame of data and connection status information that are transmitted before the connection is disconnected. When determining a condition for re-communication is meet, the first network element generates a third key based on a first key and a second key, where the first key is a key used to transmit the last frame of data, and the second key includes a key used by the first network element and the second network element to transmit each of j frames of data before the last frame of data. The first network element communicates with the second network element based on the third key, identification information of an ith frame of data, and the connection status information.