A service processing method and related devices are disclosed. The method includes: receiving, by a mobility management entity (MME), an access request message from a user equipment; determining, by the MME, whether the access request message from the user equipment is an attach message or a tracking area update request message; and if the MME has been registered as a short message serving node of the user equipment in a home subscriber server (HSS) and it is determined that the access request message is the attach message or the tracking area update request message, sending, by the MME, a notification to the HSS to inform the HSS to cancel registration of the MME as the short message serving node of the user equipment.