In order to make the data lacking in descriptions enjoy self-describing information, the IEC 61850 is applied to the modeling of distribution terminal. The protocol IEC 60870-5-104 don’t support the transmission of the self-describing information, the advantages and disadvantages of several model file mapping methods are analyzed and the extension to 104 protocol is put forward to solve the problem. The message used to transfer self-description information of devices is designed through referring to the message format of 104 protocol, which can realize the self-describing function of the distribution terminal. At the same time, a terminal description information update mechanism is proposed based on the extended 104 protocol. The feasibility of the scheme is confirmed by the test on the distribution automation system of NARI.