The invention discloses a 2.79 mu m Q-switched erbium laser dental instrument. The 2.79 mu m Q-switched erbium laser dental instrument comprises a laser power supply, a laser component, a laser water cooling system, a light guide output system, a gas and water spraying system and a central control system; the laser power supply is used for providing energy to the laser component; the laser component consists of a total-reflection chamber piece, a polarizer, a Q-switched crystal, a xenon lamp, a laser rod, a light condensing chamber, a wave plate and an output chamber piece; the laser water cooling system is used for cooling the laser rod and the xenon lamp in the laser component; the light guide output system is used for conducting laser, and is convenient to operate and use; the gas and water spraying system is used for spraying a mixture of gas and water to a laser acted tooth tissue, and has the effects of reducing the temperature of the tissue and participating laser treatment; the central control system is used for controlling the parameters of the laser power supply, the laser water cooling system and the gas and water spraying system to ensure the coordination work among the subsystems. The 2.79 mu m Q-switched erbium laser dental instrument has pulse Q-switched laser which has short pulse width and high peak power and acts the tooth tissue to improve ablation precision; meanwhile, the thermal damage to peripheral tissues also can be effectively reduced; the pain of a patient can be reduced effectively.