A method for determining an establishment cause, comprising: determining, by a Radio Resource Control, RRC, layer of a terminal, an access category of the terminal; and determining, by the RRC layer of the terminal, a connection establishment cause corresponding to the access category of the terminal, according to a mapping relationship between an access category and a connection establishment cause; characterized in that, the determining, by the RRC layer of the terminal, the access category of the terminal comprises: determining, by the RRC layer of the terminal itself, the access category of the terminal; wherein the RRC layer of the terminal acquires the mapping relationship between an access category and a connection establishment cause according to at least one of: specifications in protocols; pre-configuration; or higher-layer notification; wherein the determining, by the RRC layer of the terminal itself, the access category of the terminal, comprises: during an RRC connection resume, initiating, by the terminal, an radio access network notification area, RNA, updating procedure, and determining, by the RRC layer of the terminal itself, that the access category of the terminal is RNA update according to the RNA updating procedure. determining, by a Radio Resource Control, RRC, layer of a terminal, an access category of the terminal; and determining, by the RRC layer of the terminal, a connection establishment cause corresponding to the access category of the terminal, according to a mapping relationship between an access category and a connection establishment cause; characterized in that, the determining, by the RRC layer of the terminal, the access category of the terminal comprises: determining, by the RRC layer of the terminal itself, the access category of the terminal; wherein the RRC layer of the terminal acquires the mapping relationship between an access category and a connection establishment cause according to at least one of: specifications in protocols; pre-configuration; or higher-layer notification; wherein the determining, by the RRC layer of the terminal itself, the access category of the terminal, comprises: during an RRC connection resume, initiating, by the terminal, an radio access network notification area, RNA, updating procedure, and determining, by the RRC layer of the terminal itself, that the access category of the terminal is RNA update according to the RNA updating procedure. determining, by the RRC layer of the terminal itself, the access category of the terminal; wherein the RRC layer of the terminal acquires the mapping relationship between an access category and a connection establishment cause according to at least one of: specifications in protocols; pre-configuration; or higher-layer notification; wherein the determining, by the RRC layer of the terminal itself, the access category of the terminal, comprises: during an RRC connection resume, initiating, by the terminal, an radio access network notification area, RNA, updating procedure, and determining, by the RRC layer of the terminal itself, that the access category of the terminal is RNA update according to the RNA updating procedure. specifications in protocols; pre-configuration; or higher-layer notification; wherein the determining, by the RRC layer of the terminal itself, the access category of the terminal, comprises: during an RRC connection resume, initiating, by the terminal, an radio access network notification area, RNA, updating procedure, and determining, by the RRC layer of the terminal itself, that the access category of the terminal is RNA update according to the RNA updating procedure.