A user equipment registration method for network slice selection, adapted to a network controller having an access and mobility management function, AMF, (104, 104_1, 104_2), and the method comprising: receiving (S901, S403, S503, S603, S704, S804), by the AMF, a registration request of a user equipment, wherein the registration request comprises network slice selection assistance, NSSAI; in response to receiving the registration request, determining (S902, S404, S504, S604, S705, S805), by the access and mobility management function, whether the AMF has a capability for serving the user equipment according to the slice selection information; if having the capability for serving the user equipment is determined, transmitting, by the AMF, a first network function discovery request including the NSSAI to a network function repository function, and in response to receiving, by the AMF, a network function discovery response corresponding to the first network function discovery request, selecting, by the AMF, (S903, S408, S512, S614, S709, S810) a network function for serving the user equipment according to the network function discovery response to perform a registration setting operation with the selected network function, wherein the network function discovery response includes at least one candidate network function associated with at least one candidate network slice, wherein the at least one candidate network function is determined according to the NSSAI in the registration request; and if not having the capability for serving the user equipment is determined, transmitting, by the AMF, a second network function discovery request for searching a target access and mobility management function (104_2) to the network function repository function, and in response to receiving another network function discovery response corresponding to the second network function discovery request from the network function repository function, transmitting, by the AMF, (S507, S609) an interface connection release message and information regarding a target access and mobility management function to an access node, wherein the another network function discovery response includes the target access and mobility management function. receiving (S901, S403, S503, S603, S704, S804), by the AMF, a registration request of a user equipment, wherein the registration request comprises network slice selection assistance, NSSAI; in response to receiving the registration request, determining (S902, S404, S504, S604, S705, S805), by the access and mobility management function, whether the AMF has a capability for serving the user equipment according to the slice selection information; if having the capability for serving the user equipment is determined, transmitting, by the AMF, a first network function discovery request including the NSSAI to a network function repository function, and in response to receiving, by the AMF, a network function discovery response corresponding to the first network function discovery request, selecting, by the AMF, (S903, S408, S512, S614, S709, S810) a network function for serving the user equipment according to the network function discovery response to perform a registration setting operation with the selected network function, wherein the network function discovery response includes at least one candidate network function associated with at least one candidate network slice, wherein the at least one candidate network function is determined according to the NSSAI in the registration request; and if not having the capability for serving the user equipment is determined, transmitting, by the AMF, a second network function discovery request for searching a target access and mobility management function (104_2) to the network function repository function, and in response to receiving another network function discovery response corresponding to the second network function discovery request from the network function repository function, transmitting, by the AMF, (S507, S609) an interface connection release message and information regarding a target access and mobility management function to an access node, wherein the another network function discovery response includes the target access and mobility management function.