The invention relates to an overload yarn tension buoy. The buoy comprises an upper cap and a lower cap, which are sleeved together, wherein the upper and lower caps are buckled with each other to form an inner cavity; springs are arranged in the inner cavity; the two ends of the springs respectively push against the inner walls of the upper and lower caps; the lower cap is fixed; the upper cap can float up and down according to the pressure applied by a yarn; a pressure slot for the yarn to pass through is formed in the top of the upper cap; a guide wheel is arranged in the pressure slot; a cutter bar is fixed inside the lower cap; the free end of the cutter bar is close to the guide wheel in the inner cavity.