The invention discloses an adjustable manual valve seat reamer. The adjustable manual valve seat reamer is composed of hand wheels, a guide rod, a guide sleeve, a knife feeding plate, a knife rest anda supporting frame, and is characterized in that a cylinder-shaped cavity bolt is arranged in the middle of a vertical guide rod, and a bearing is installed at the upper end of the cavity bolt, a locking nut cooperating with the cavity bolt is arranged on the periphery of the upper part of the cavity bolt, and a spherical guide sleeve is installed in a cavity of the cavity bolt; the knife feedingplate is installed above the cavity bolt; and the inner cavity of the knife feeding plate is provided with four equal-part taper feeding nuts, inverted T-shaped guide sleeves extending upwards are installed on the knife feeding nuts, the upper ends of the inverted T-shaped guide sleeves are connected with the hand wheels, the lower end faces of the knife feeding plates are provided with T-shapedfeeding knife pressing covers which are connected with the knife feeding nuts, the lower ends of the knife pressing covers are conical, a machine base is installed on the lower surface of the cavity bolt, and the machine base is divided into an upper part and a lower part. The problem that time and labor are wasted and the valve sealing effect is poor when the valve seat is repaired by grinding issolved, and the adjustable manual valve seat reamer is suitable for repairing and using in various engine valve seats.