The invention relates to the technical field of data communication, in particular to a data transmission method and system. The data transmission method and system are used for solving the problem that the secrecy degree of a data server for client files is low. The data transmission method includes that receiving a write-in request message with user name, file name and file size from a client; confirming an encryption key, a division strategy and the corresponding relationship between each data block name and the data server according to the write-in request message and feeding back; enabling the client to send the encryption key, and the data and names of the divided data blocks to the corresponding data server to perform encryption storage; receiving a read request message with user name and file name from the client; confirming a decryption key and the corresponding relationship between the name of each data block of the file and the data server according to the read request message and feeding back to enable the client to send the decryption key and the names of the data blocks to the corresponding data server to obtain the data of the corresponding data blocks performed with decryption.