The invention is concerned with the data transmission method and the system, it is: the user's terminal or the base station as the sending side, the corresponding base station or the user's terminal as the receiving side, the sending side process code for the information bit in order to get the code block number equal with the biggest resend time, the sending side divides the code block number into at least two groups, and at least the first group includes two code block; sets the transmission time slot of each code block in the group, and sends to the receiving side; the receiving side receives code block and decode, after receiving a group of code block, if the decode is still incorrect, feedbacks once NACK. The invention can reduce the feedback signaling overhead effectively, improve the utilance of the channel resource.