The invention discloses a constant temperature control device for an ultrasonic crusher and a control method thereof. The device comprises a glass reaction device having a jacket, a first temperature sensor, a second temperature sensor, a controller, a driving module, a valve motor and an electrically-operated valve. A water inlet of the glass reaction device having the jacket is connected with a water inlet pipe; the water inlet pipe is provided with the electrically-operated valve; a water outlet of the glass reaction device having the jacket is provided with the first temperature sensor; a reaction tank of the glass reaction device having the jacket is internally provided with the second temperature sensor; the signal output ends of the first temperature sensor and the second temperature sensor are connected with a signal input port of the controller; a signal output port of the controller is connected with a signal input port of the driving module; and the driving module drives the valve motor of the electrically-operated valve. The constant temperature control device can obtain faster response speed, smaller overshoot and higher anti-interference capability.