The invention discloses a composite catalytic electrode for producing oxygen by electrolyzing water, and a preparation method and application thereof. The electrode expression is Ni(OH)2/Ni3S2/Ni, wherein a Ni(OH)2 lamina is used as an outer layer coating layer, Ni3S2 nanoparticles are used as an active substance, and Ni foam is used as a conducting substrate. The preparation method comprises the following steps: carrying out ultrasonic cleaning on a metal nickel source sequentially with deionized water, alcohol and acetone; impregnating the pretreated metal nickel source in a sulfur source water solution, adding into a high-pressure autoclave, and carrying out hydrothermal reaction at 140-200 DEG C for 1-8 hours; and cooling, taking out the sulfurized metal nickel, rinsing with deionized water, and carrying out vacuum drying. The composite electrode for electrolyzing water has ultralow water electrolysis overpotential and high current density, obviously reduces the electric power consumption, and thus, has important application in the field of water electrolysis. Meanwhile, the composite electrode synthesis method is simple, has the advantage of low cost for raw materials and synthesis, and is suitable for application in water electrolysis industry.