A streaming media data transmission system comprising a client and a server; the client comprising: a first processing module configured to determine whether the server distributes a plurality of segments with same content and different code rates according to different values of a third indication information sent by the server; and a second processing module configured to, when the first processing module determines that the server distributes a plurality of segments with same content and different code rates, determine whether the server transmits a segment with a high code rate first or transmits a segment with a low code rate first according to a first indication information sent by the server and used to indicate whether the server transmits the segment with the high code rate first, and further configured to generate a second indication information for reporting receipt status of the segment to the server; and the server comprising: a processing module configured to determine whether a segment with a high code rate is transmitted first or a segment with a low code rate is transmitted first when a plurality of segments with same content and different code rates are to be distributed to a client, and configured to adjust the transmission of the segments according to the said second indication information sent by the client; and a transceiver module configured to send the third indication information and then send the first indication information to the client, and configured to receive the second indication information sent by the client after sending the first indication information to the client, wherein, the first indication information, the second indication information and the third indication information are carried in messages extended over the WebSocket protocol with respect to the MPEG DASH standard and transmitted through the WebSocket text frames. the client comprising: a first processing module configured to determine whether the server distributes a plurality of segments with same content and different code rates according to different values of a third indication information sent by the server; and a second processing module configured to, when the first processing module determines that the server distributes a plurality of segments with same content and different code rates, determine whether the server transmits a segment with a high code rate first or transmits a segment with a low code rate first according to a first indication information sent by the server and used to indicate whether the server transmits the segment with the high code rate first, and further configured to generate a second indication information for reporting receipt status of the segment to the server; and a first processing module configured to determine whether the server distributes a plurality of segments with same content and different code rates according to different values of a third indication information sent by the server; and a second processing module configured to, when the first processing module determines that the server distributes a plurality of segments with same content and different code rates, determine whether the server transmits a segment with a high code rate first or transmits a segment with a low code rate first according to a first indication information sent by the server and used to indicate whether the server transmits the segment with the high code rate first, and further configured to generate a second indication information for reporting receipt status of the segment to the server; and the server comprising: a processing module configured to determine whether a segment with a high code rate is transmitted first or a segment with a low code rate is transmitted first when a plurality of segments with same content and different code rates are to be distributed to a client, and configured to adjust the transmission of the segments according to the said second indication information sent by the client; and a transceiver module configured to send the third indication information and then send the first indication information to the client, and configured to receive the second indication information sent by the client after sending the first indication information to the client, wherein, the first indication information, the second indication information and the third indication information are carried in messages extended over the WebSocket protocol with respect to the MPEG DASH standard and transmitted through the WebSocket text frames. a processing module configured to determine whether a segment with a high code rate is transmitted first or a segment with a low code rate is transmitted first when a plurality of segments with same content and different code rates are to be distributed to a client, and configured to adjust the transmission of the segments according to the said second indication information sent by the client; and a transceiver module configured to send the third indication information and then send the first indication information to the client, and configured to receive the second indication information sent by the client after sending the first indication information to the client, wherein, the first indication information, the second indication information and the third indication information are carried in messages extended over the WebSocket protocol with respect to the MPEG DASH standard and transmitted through the WebSocket text frames.