The invention discloses an anion constant-humidity water filtering device which comprises a shell, a water tank, a water curtain device, a cylinder type air duct, a motor, a fan, an anion module, an air inlet and an air outlet, wherein the air inlet is formed in the side wall of the lower part of the shell, the air outlet is formed in the side wall of the top or the upper part, a base is sealed; the anion module is arranged on the inner wall of the shell and at the inner side of the air inlet, an anion generator is arranged in the anion module, the anion generator is electrically connected with a carbon brush; the water tank is arranged at the lower part in the shell and is filled with water; the water curtain device is arranged in the middle in the shell and above the water tank, the lower end of the water curtain device extends into the water tank, the lower edge of the water curtain device is lower than the upper edge of water in the water tank; the water curtain device is a cone thick in upper part and thin in lower part, the water curtain device is hollow inside, and spiral and convex ribs are arranged on the inner wall; a plurality of through holes are formed in the wall of the water curtain device and between adjacent ribs, the through holes are divided into an upper layer and a lower layer, water mist holes are at the lower layer, and large water drop holes are at the upper layer; the cylinder type air duct is arranged in the middle in the shell and at the periphery of the water curtain device, and extends into the water tank, and the lower edge of the cylinder typeair duct is higher than the upper edge of water in the water tank.