The invention relates to a water-cooling variable-frequency combustion device for biomass fuels, which comprises a water-cooling vibrating grate, a variable-frequency motor, a spring supporter, a flexible cooling pipe, an air supply chamber and an ash chamber, wherein the water-cooling vibrating grate is obliquely supported on a base by the spring supporter; the gradient of the water-cooling vibrating grate is adjusted through the spring supporter; the water-cooling vibrating grate is connected to the variable-frequency motor and is excited by the variable-frequency motor; a vibration speed of the water-cooling vibrating grate can be controlled by adjusting the frequency of the variable-frequency motor; the water-cooling vibrating grate is respectively connected to front and back water-cooling wall headers or a cooling water outlet and a cooling water inlet through front and back flexible connecting pipes; a feeding mechanism is arranged above and in front of the water-cooling vibrating grate; the ash chamber is arranged behind and under the water-cooling vibrating grate; and the air supply chamber is arranged on the bottom of the water-cooling vibrating grate. The device can be used for solving the problem of efficiently, stably and cleanly combusting the biomass fuels which are high in volatile matter, low in ash content and low in ash melting point. The device has the advantages of clean combustion, high efficiency, excellent fuel adaptability, high automation degree, low cost, safety, reliability, long service life, and the like.