The present disclosure relates to a high-strength concrete and a preparation method thereof. The high-strength concrete includes lignin, recycled fine powder, cement, water, sand, gravels and a water reducing agent. The recycled fine powder is recycled fine powder of discarded concrete, and is prepared by separating solid waste of discarded buildings, then performing impurity removal and crushing processing, and grinding same by a ball mill into dust with a particle size of less than 0.16 mm. The lignin is discarded wood lignin, which is prepared by crushing the wood, stirring and extracting a sodium hydroxide aqueous solution with a mass concentration of 5% for 1 to 2 hours at the temperature of 80 DEG C. to obtain a black lignin alkali solution, adding a hydrochloric acid solution with a mass concentration of 30% into the alkali solution for stirring, and making the pH reduced to 7.0 for standing and layering.