The invention discloses a synchronous grouting material used for a tunnel and a preparation method thereof. The grouting material is the grout which is prepared by taking sediment grout as a main raw material, wherein the sediment grout comprises 30 to 65 percent of clay and fine sand totally and the weight ratio of soil to sand in the sediment grout is 0.1-0.18:1; and adding 80 to 120 kg of cement, 300 to 450 kg of coal ash, 200 to 500 kg of water or mud water and 3 to 10 kg of sodium carboxymethyl cellulose into per cubic meter of the sediment grout, wherein the grout density is between 1.85 and 2.05 g/cm<3> and the grout consistency is between 10.5 and 12 cm. In the preparation method, sediment and the mud water generated in a construction process are adopted as grouting materials, so that the sediment and the mud water can be changed into treasure from waste; and therefore, the preparation method has the characteristics of great reduction of the dosage of high-energy consumption cement, capability of working inside and outside tunnels, and convenient construction.