The invention provides an automatic dosing device for an oil well. The automatic dosing device comprises a medicament box and a mechanical dosing component, the mechanical dosing component is composed of a cylinder body, a rod body piston component and a check valve, the rod body piston component comprises a striking rod, a piston and a striking head, the striking head is arranged at the top end of the striking rod, a first reset spring is arranged below the striking head, the piston is arranged on the lower portion of the striking rod, the piston and the lower portion of the striking rod are arranged in a first inner cavity of the upper portion of the cylinder body, the piston is driven by the striking rod to slide along the first inner cavity, the check valve is arranged in a second inner cavity of the lower portion of the cylinder body, and a second reset spring is arranged. A drug inlet is formed in the side wall of the first inner cavity, and the drug inlet is connected with the medicament box. The device achieves automatic dosing of the oil well, and is simple in structure and obvious in effect, and the operation of the field mounting and dismounting is convenient.