A method for configuring network slice indexes, being applied to a network side device and comprising: configuring (S201) corresponding Shortened Slice Indexes, SSIs, for Network Slice Selection Assistance Information, NSSAI, of a first type of network slices based on a set partition granularity, wherein NSSAI of a network slice and an SSI corresponding to the NSSAI indicate the same network slice, and a length of the NSSAI is longer than a length of the SSI corresponding to the NSSAI; and sending (S202) a downlink message bearing the NSSAI and the corresponding SSIs of the first type of network slices to User Equipment, UE; wherein the set partition granularity at least comprises one of: taking a Tracking Area, TA, as a granularity and taking a Routing Area, RA, as a granularity; characterized in that when the UE is registered to multiple TAs and the set partition granularity comprises taking the TA as the granularity, configuring (S201) the corresponding SSIs for the NSSAI of the first type of network slices based on the set partition granularity comprises: determining, according to a number of first type of network slices in respective TA, an SSI length in the respective TA; and based on the SSI length in the respective TA and the respective TA where the NSSAI of the first type of network slices are located, configuring the corresponding SSIs for the NSSAI of the first type of network slices; or, when the set partition granularity comprises taking the RA as the granularity, configuring (S201) the corresponding SSIs for the NSSAI of the first type of network slices based on the set partition granularity comprises: determining, according to a number of first type of network slices in respective RA, an SSI length in the respective RA; and based on the SSI length in the respective RA and the respective RA where the NSSAI of the first type of network slices are located, configuring the corresponding SSIs for the NSSAI of the first type of network slices configuring (S201) corresponding Shortened Slice Indexes, SSIs, for Network Slice Selection Assistance Information, NSSAI, of a first type of network slices based on a set partition granularity, wherein NSSAI of a network slice and an SSI corresponding to the NSSAI indicate the same network slice, and a length of the NSSAI is longer than a length of the SSI corresponding to the NSSAI; and sending (S202) a downlink message bearing the NSSAI and the corresponding SSIs of the first type of network slices to User Equipment, UE; wherein the set partition granularity at least comprises one of: taking a Tracking Area, TA, as a granularity and taking a Routing Area, RA, as a granularity; characterized in that when the UE is registered to multiple TAs and the set partition granularity comprises taking the TA as the granularity, configuring (S201) the corresponding SSIs for the NSSAI of the first type of network slices based on the set partition granularity comprises: determining, according to a number of first type of network slices in respective TA, an SSI length in the respective TA; and based on the SSI length in the respective TA and the respective TA where the NSSAI of the first type of network slices are located, configuring the corresponding SSIs for the NSSAI of the first type of network slices; or, when the set partition granularity comprises taking the RA as the granularity, configuring (S201) the corresponding SSIs for the NSSAI of the first type of network slices based on the set partition granularity comprises: determining, according to a number of first type of network slices in respective RA, an SSI length in the respective RA; and based on the SSI length in the respective RA and the respective RA where the NSSAI of the first type of network slices are located, configuring the corresponding SSIs for the NSSAI of the first type of network slices <EOS>