In an aspect of the present invention, a method for a user equipment to update a policy in a wireless communication system may include transmitting a first registration request message to an access and mobility management function (AMF), wherein the first registration request message includes requested network slice selection assistance information (NSSAI) including single (S)-NSSAI corresponding to a network slice with which the user equipment wants to register; receiving a first registration accept message as a response to the first registration request message from the AMF, wherein the first registration accept message includes an allowed NSSAI including at least one S-NSSAI allowed by the AMF; and requesting the update of a network slice selection policy (NSSP) associated with new S-NSSAI from the AMF when the new S-NSSAI not included in the requested NSSAI is included in the allowed NSSAI and the NSSP associated with the new S-NSSAI is not present.