NOVELTY - The method comprises passing biogas through a gas pressurizing device having a pressure of greater than or equal to 2 MPa, then passing into a water washing tower to remove carbon dioxide and hydrogen sulfide, where air flow rate of the marsh gas is 4-6 m3/hour, and an inner pressure of the water washing tower is greater than or equal to 1 Mpa, preferably 1-1.2 Mpa. The water washing tower comprises at least two layers, preferably three layers and a tower body, where the lower layer of the tower is provided with a liquid storage section.    USE - The method is useful for biogas purification using water (claimed).    ADVANTAGE - The method economically and conveniently purifies the biogas by water washing and removing carbon dioxide and hydrogen sulfide gas in biogas with low energy and water consumption, and without discharge in the biogas.    DETAILED DESCRIPTION - The method comprises passing biogas through a gas pressurizing device having a pressure of greater than or equal to 2 MPa, then passing into a water washing tower to remove carbon dioxide and hydrogen sulfide, where air flow rate of the marsh gas is 4-6 m3/hour, and an inner pressure of the water washing tower is greater than or equal to 1 Mpa, preferably 1-1.2 Mpa. The water washing tower comprises at least two layers, preferably three layers and a tower body, where the lower layer of the tower is provided with a liquid storage section whose bottom end is provided with a water discharging valve and upper end is provided with an air inlet. The liquid storage section is further provided with two level windows at the upper section. The window is located above the water washing tower. The top part of the tower is provided with a water spraying device. The water spraying device comprises a pipe mounting on a tube and a nozzle in the tower. A water inlet of the tube extends out of the tower. The upper layer of the tower is provided with a demisting section. A top end of the water washing tower is provided with an exhaust valve via a pipeline. The water washing tower comprises a water distributor whose water inlet is connected to a water storage tank through the pipeline. The water distributor is connected with a pump. The exhaust valve and water discharging valve are opened when the water level reaches above the liquid level in the tank. The water flow quantity of the water spraying device is less than 0.6 m3/hour, preferably 0.6-0.72 m3/hour. The method comprises exiting biogas, which is rich in carbon dioxide and hydrogen sulfide gas from the exhaust valve, and then passing the biogas into water column for elution of carbon dioxide and hydrogen sulfide. The tower body is two-sided glass body and includes a glass cylinder main body formed with a hole.