The invention provides a preparation process of a cement grinding aid without changing standing thickening water demand of cement. The process comprises the following steps: S01: weighing various preparative raw materials in parts by weight, adding water into a reactor, adding thiosulfate while stirring, and stirring for an hour; S02, continuously adding carbonyl coke aldehyde derivatives, composite carboxyl alcohol amine, polyhydric alcohols and molasses sequentially; uniformly stirring, and continuously stirring for an hour; S03, adding the residual preparative raw materials, and continuously stirring for an hour, thereby obtaining the product. According to the cement grinding aid prepared by the process disclosed in the invention, the standing thickening water demand of cement is not changed, and interaction with concrete admixtures is improved; due to absence of chloride ions, corrosion on reinforcements in concrete is reduced, and the durability and erosion resistance of the concrete are increased.