Pressure-filtered electrolyzer is the key equipment in the process of hydrogen production from water electrolysis. Spherical convex–concave structure is arranged in the microchannel of electrolyzer plate. The distribution of water flow in the microchannel directly affects the distribution of electrolyte and heat transfer, thus affecting the stability of the electrolyzer. In order to study the flow field characteristics in the plate channel of pressure-filtered water electrolyzer, the RNG k?? turbulence model was used to simulate the flow field in the single pole chamber of the electrolytic units, and the eddy generated in the channel and the uniformity of velocity distribution were analyzed. The results showed that the structure of the plate passage determined the location of the eddy, which affected the velocity distribution in the passage. With the increase of the mass flow rate, the intensity of the eddy increased and the disturbance degree increased. The velocity distribution of the flow was symmetrical, and the curve of velocity distribution caused by the spherical convex–concave structure had fluctuation. There were peak velocities at the edge positions of different spherical convex structures. The uniformity index of velocity distribution along the flow direction was different under various flow conditions. The disturbance effect of spherical convex–concave structure could improve the uniformity of velocity distribution, but the improvement effect was different under various flow conditions.