The invention relates to a solid polymer electrolyte membrane water electrolyzer which comprises more than two bipolar plates and membrane electrodes arranged between each two bipolar plates, conductive plates, insulating plates and end plates are respectively arranged at two ends of the bipolar plate at the outermost layer, and the plates are fastened into a whole by screw rods and nuts. The solid polymer electrolyte membrane water electrolyzer is characterized in that a hydrogen channel is arranged at the center of the electrolyzer which is fastened into the whole; each bipolar plate is formed by compounding an anode side flow field plate and a cathode side flow field plate; and a plurality of ridges and runners which are parallel to the ridges are arranged on an anode side flow field, equidistant openings are arranged on each ridge, and the opening of the upper row of the ridges are opposite to the center of the lower row of the ridges. The electrolyzer can lead water to evenly pass through the flow fields and be further distributed on the surfaces of the membrane electrodes, simultaneously take out a product of hydrogen, reduce the volume of the electrolyzer, reduce the weight of the electrolyzer, improve the polarization performance of the water electrolyzer and prolong the service life of the water electrolyzer.