The utility model discloses a precision adjusting device of a flow meter. The precision adjusting device is formed by combination of an input transmission shaft, adjusting rings, an adjusting shaft, steel balls, springs and a transmission output shaft in an organic mode. The input transmission shaft is installed in a cavity at the lower end of the adjusting shaft, the steel balls are arranged on the outer circle of the adjusting shaft, and the springs and the steel balls are connected through steel ball pressing rings. Steel ball inner rings are arranged on the lower side of the steel balls, a bearing is sleeved on the outer side of the lower end of the adjusting shaft, a blanking cap is arranged in the inner side of the transmission output shaft, shaft sleeves are arranged between the transmission output shaft and the steel balls, a check ring used for a hole is arranged at the upper ends of the shaft sleeves, a dial component is installed at the upper end of the check ring for the hole, and the number of the steel balls is six. A check ring for a hole and a check ring for a shaft are installed at the lower end of the bearing, matching surfaces of the adjusting shaft and the steel balls are circular conical surfaces, and the adjusting rings and the steel ball pressing rings are connected through spring pins. The precision adjusting device of the flow meter has the advantages of being compact in structure, stable and reliable in performance, wide in application range, long in service life, easy and convenient to operate, convenient to use and the like.