The invention relates to a synchronous grouting material of shield tunneling and its preparation method. A cement-free anti-water dispersion and anti-water corrosion synchronous grouting material is mainly composed of the following components by weight ratio: 250-350kg/m<3> of phosphogypsum, 250-400kg/m<3> of fly ash, slag powder and steel slag powder, 25-40kg/m<3> of attapulgite clay, 1-1.4kg/m<3> of polyacrylamide, 2-2.8kg/m<3> of an aliphatic high efficiency water reducer, 800-1000kg/m<3> of river sand, and 200-400kg/m<3> of water. Specifically, for the sum of the weight of the fly ash, the slag powder and the steel slag powder, the fly ash accounts for 0.5-99%, the slag powder accounts for 0.5-99%, and the steel slag powder accounts for 0.5-99%. Mixing and stirring of the materials can obtain the required synchronous grouting material, which has the characteristics of anti-water dispersion, anti-water corrosion, good fluidity, good construction performance, no pipe blockage, long usable time, and fast increase of later strength.