The present application provides a congestion processing method and device. The method includes: an access network device receives a first message transmitted by a source core network device, where the first message is used for indicating that the source core network device is overloaded; and the access network device, according to the first message, performs an operation of migrating the terminal device from the source core network device to a target core network device, where the target core network device and the source core network device support different communication systems. The congestion processing method according to the present application can solve the congestion problem of a core network device, realize load balancing between core network devices, and thereby improving user experience.