Abstract: A data transmission coordination system and a method thereof are provided. In the method, multiple terminal devices are grouped into a first sub-group and a second sub-group. The first and the second sub-groups respectively include at least one of the terminal devices and have different data transmission modes for uploading data. The power consumption of the data transmission mode of the first sub-group is higher than that of the second sub-group. In response to the first terminal device of the sub-group conforming to a replacement condition, a second terminal device of the second sub-group replaces the first terminal device, so that the first sub-group includes the second terminal device. The replaced first terminal device is associated to the second sub-group or not able to transmit depending on an operation situation. Accordingly, a whole lifetime of the system is increased.