The present invention provides methods for transmitting SyncML synchronization data. One is that the originator constructs a SyncML message after encrypting the user data to be transmitted and then transmits the data in an existing transmission way; the user data includes, but is not confined to, authentication information, terminal capability information and the data to be synchronized; the other method is that the originator encrypts the SyncML message in the transport layer before transmitting the message, and the recipient deciphers the received SyncML message from transport layer and processes the message subsequently. The two methods can be used either separately or together. If they are used together, the transmission of SyncML synchronization data is provided with double safety insurance. By using the present invention, user data can be transmitted safely without being intercepted by the third party.