The utility model discloses a marking auxiliary tool. The marking auxiliary tool comprises a tool main body, an adjusting block and a prefix fixing block. The tool main body comprises a circular ring with a gap and a strip-shaped groove which is fixedly arranged at the circular ring gap position along a central axis direction of the circular ring. The upper end and the lower end of the strip-shaped groove are both provided with an opening, and the opening in the lower end is opposite to the gap of the circular ring in an up-down mode. The adjusting block is arranged inside a groove body of the strip-shaped groove and can slide along the length direction of the groove body. The adjusting block comprises a square barrel body and a fixing device, wherein the upper end and the lower end of the square barrel body are both provided with an opening, and the fixing device fixes the square barrel body on the strip-shaped groove. The prefix fixing block is a square barrel body and is arranged inside the square barrel body of the adjusting block, wherein the upper end and the lower end of the prefix fixing block are both provided with an opening. The marking auxiliary tool is accurate in marking positioning and good in prefix righting effect.