A process for synthesizing cross-linked poly(sodium acrylate) as high-absorption resin using acrylic acid, sodium hydroxide and dicarbonate as raw materials by one-step polymerizing and neutralizing in an open reactor includes replacing air in the system with CO2 as hy-product, adding single-component initiator, heating and foaming polymerization. Its advantages are simple process and equipment, stable water-absorbing factor, less residual monomer and low cost.