The present invention relates to tunnel-wall post-injection pulp material and a preparation method of the tunnel-wall post-injection pulp material. Tunnel back-lining pulp-injection material that can prevent the upward-floating of the duct piece is characterized in consisting of a substrate compound A and an additive compound B, wherein, the substrate compound A includes cement, fly ash, sand and water; the additive compound B includes silicone ash, swell soil, droxyethylcellulose, polyacrylamide, sulfamate, naphthaline water-reducing agent and gluconic acid sodium salt; the ratio of the ingredients (kg/m<3>): 100 to 200 portions of cement, 300 to 600 portions of fly ash, 800 to 1600 portions of sand, 280 to 560 portions of water, 10 to 40 portions of silicone ash, 12 to 30 portions of swell soil, 0.4 to 0.8 portions of droxyethylcellulose, 0.2 to 0.4 portions of polyacrylamide, 0.2 to 0.4 portions of sulfamate, 1.6 to 2.9 portions of naphthaline water-reducing agent and 0.2 to 0.4 portions of gluconic acid sodium salt. The present invention can realize the high stability, high water dispersion prevention, high-efficient water-reducing plasticity preservation and adjustable performance of the pulp-injection material the condensation under the conditions of high water pressure and water satuation, thereby greatly improving the working performance and the durance of the pulp-injection material.