A user equipment registration method for network slice selection, and a network controller and a network communication system are provided. The method includes: receiving a registration request of a UE; in response to receiving the registration request including slice selection information, determining whether having a capability for serving the UE according to the slice selection information, so as to transmit a first network function discovery request including the slice selection information or transmit a second network function discovery request for searching a target AMF; and selecting a network function for serving the UE according to a network function discovery response to perform a registration setting operation after receiving the network function discovery response corresponding to the first network function discovery request, or transmitting an interface connection release message to an access node after receiving another network function discovery response corresponding to the second network function discovery request.