The invention relates to a synchronous slip casting material and a preparation method for tunnels, in particular to a sulphoaluminate cement base synchronous slip casting material, which is characterized in that the sulphoaluminate cement base synchronous slip casting material is prepared by a basal body component and an externally-mixing component, wherein the basal body component comprises sulphoaluminate cement, coal ash, powdered ore, sand and water, the externally-mixing component comprises polycarboxylic acids highly-effective water reducing agent, sodium bentonite and triethanolamine early-strength admixture, the proportioning (kg/m3) of each component is that sulphoaluminate cement: 100-200, coal ash: 300-400, powdered ore: 45-455, sand: 700-1200, water: 350-500, polycarboxylic acids highly-effective water reducing agent: 3.0-4.0, sodium bentonite: 40-60, and triethanolamine early-strength admixture: 0.05-0.2. The synchronous slip casting material prepared by the method has the characteristics of excellent early-stage intensity, underwater non-dispersibility, permeability-resisting and corrosion resistance, and can be used in large-scale river-sea-crossing tunnels or underground engineering.