A method and an apparatus for initiating user plane path re-establishment and a communications system are disclosed. The method includes: determining, by a session management function entity based on first location information of a terminal device, a session service area to which a current session of the terminal device belongs; and after receiving second location information of the terminal device sent by a mobility management function entity, if determining that the second location information is not within the session service area, instructing the terminal device to initiate a re-establishment procedure for the current session or initiate a handover procedure. Due to introduction of the session service area, when the terminal device moves back and forth at edges of service areas of two adjacent user plane function entities, a ping-pong effect caused by frequent handover between the two user plane function entities is avoided, and user experience is improved.