The embodiment of the application relates to registration and session establishment methods, a terminal and an AMF (Access and
Mobility Management Function) entity. The session establishment method comprises the following steps that: a terminal sends a first message to the AMF entity, wherein the first message includes first information, first network
slice selection information and second networkslice selection information, the first information includes information for requesting the establishment of a
protocol data unit (PDU) session, the first network
slice selection information is used by the AMF entity to select a first
session management control function (SMF) entity, and the second network
slice selection information is used by the AMF entity to select a second SMF entity; and theterminal receives a second message sent by the AMF entity, wherein the second message includes second information, and the second information includes information accepted by PDU session establishment. Through adoption of the registration and session establishment methods, the AMF entity can accurately determine S-NSSAI (Single Network
Slice Selection Information) during establishment of the PDUsession in order to completes the establishment of the PDU session.