A data transmitting method for wireless communication system applied in a transmitting device for transmitting a number of data packets to a receiving device is provided. Firstly, n data packets are transmitted to the receiving device during the first time period, wherein n is a nature number. Next, the first accumulated number is recorded, wherein the first accumulated number denotes the times of resending the n data packets during the first time period. Then, determine that whether the first accumulated number exceeds a predetermined value or not. If the first accumulated number exceeds the predetermined value, then other communication methods are adopted and the method carries on transmitting the remaining data packets; if the first accumulated number does not exceed the predetermined value, the first accumulated number is cleared, and the method carries on transmitting the remaining data packets to the receiving device.