The invention provides a mechanical self-locking type steam water mixing valve. The mechanical self-locking type steam water mixing valve comprises a valve body, a left end cover and a right end cover. The valve body comprises a steam inlet hole, a water inlet hole and a water outlet hole I. An isolation plate I and an isolation plate II are arranged in the valve body. An inner cavity of the valve body is divided by the isolation plate I and the isolation plate II into a cavity body I, a cavity body II and a cavity body III. A left nut is arranged in the cavity body I, a plunger shaft I is arranged in an inner hole III of the left end cover, and a spring I is arranged between the plunger shaft I and the inner wall of the left end cover. An air inlet nut is arranged in the cavity body II. A plunger shaft II is arranged in a cavity of the air inlet nut. A water inlet valve is arranged on the left side of a water inlet hole of the cavity body III. A right nut is arranged on the right side of the water inlet valve in the cavity body III. A right screw rod is arranged in an inner hole IV in the right end cover. The mechanical self-locking type steam water mixing valve is safe, the temperature is adjustable, and the temperature can be measured in real time.