Embodiments of this application provide a packet transmission method, a communication apparatus, and a communication system. A target transport layer proxy network element establishes a fourth transport layer connection based on a first context of a source transport layer proxy network element, where the first context is a context about packet transmission of the source transport layer proxy network element on a first path. If the target transport layer proxy network element receives first indication information, and the first indication information indicates that application context migration between a first application server and a second application server is completed, the target transport layer proxy network element performs transport layer processing on a packet on a second path based on a second context of the target transport layer proxy network element, and transmits, on the second path, a packet obtained through the transport layer processing. Hence, a packet loss can be avoided.