The invention discloses a preparation method for a gas making barrier of an anti-adsorption type polycarboxylic acid water reducer. The preparation method comprises the following steps: 1) placing a polyether macromonomer and water at the bottom of a reactor, stirring until a solution has no obvious blocky or sheet-shaped materials, controlling the initial temperature to be not higher than 22 DEGC, and adjusting the pH to be equal to 8.5 with liquid alkali; 2) after 5 min, simultaneously dropwise adding a reducing chain transfer complex agent solution and an oxidant solution, and controllingthe dropping time to be a h; 3) after another 5 min, dropwise adding a small monomer solution, and controlling the dropping time to be a to 0.5 h; 4) then after 20 min, dropwise adding a liquid alkalisolution, controlling the dropping time to be a+0.5 h; 5) at later reaction, when the reaction temperature exceeds 35 DEG C, opening cooling water to circulate, and opening an air pump and introducing micro pores of which the apertures are 0.5 to 2 mm to the reaction kettle; and 6) after dropwise adding the liquid alkali solution, carrying out heat preservation for 0.5 to 2.0 h, stopping stirring, thus obtaining finished product mother liquor. The polycarboxylic acid water reducer disclosed by the invention has strong adaptability, can resist burying or physical adsorption of strong adsorbates, and obviously improves the slump retention, cohesiveness and plasticity retention of fresh concrete.