This application relates to a yarn carrier device with a yarn tension control function for a flat knitting machine, and a yarn tension control method. At the moment a carriage is connected to a yarn carrier device, a fixing frame carrying a bobbin ascends or descends on sliding rails installed on the yarn carrier device. The ascending or descending speed, time and distance of the fixing frame can be calculated directly according to a yarn carrier stop, the quantity of an unknitted portion of the yarn and the speed of the carriage. When the carriage contacts a yarn carrier, the fixing frame is controlled to ascend along the sliding rails. When the carriage drives the yarn carrier to enter a knitting area, the fixing frame is controlled to descend.