The present invention relates to a mechanical children lock for a microwave oven, including a rotation turnbutton, a mounting plate with springs, a cam is provided with the rotation turnbutton, a side wall of the cam is provided with a slot, the external side of the cam is provided with a position-limiting plate and a power supply switch, the position-limiting plate is provided with a L-shaped claw, and the contact of the power supply switch collides an involute arc face of the cam external wall. The structure of the lock is simple, and it is easy to implement; by a special mechanism, when the rotation turnbutton is rotated to a certain position, the turnbutton is pressed according to a certain journey and is then rotated with a certain angle, the microwave oven will be in the children lock state. At this moment, the total power supply of the microwave oven is disconnected, a rotary shaft is locked, and thus it is capable of implementing a children lock function effectively.