The invention discloses a high-content manganese additive used for producing aluminum alloy and a preparing method of the high-content manganese additive. The manganese additive in a cake shape or rugby shape and formed by pressing raw material powder. The raw material powder comprises manganese powder, aluminum powder, iron powder and fluxing agents. The manganese powder, the aluminum powder, the iron powder and the fluxing agents are crushed under protection of inert gas, and the high-content manganese additive further comprises a surfactant. According to the high-content manganese additive, by mass, the manganese powder accounts for 86%-97%, the aluminum powder accounts for 2.39%-6.39%, the iron powder accounts for 0%-6%, the fluxing agents account for 0.01%-0.05%, and the surfactant accounts for 0.5%-2%. The density of the formed high-content manganese additive ranges from 3.0 g/cm<3> to 5.0 g/cm<3>. The method includes the steps of 1, crushing, 2, material preparing, 3, material mixing, 4, pressing, 5, drying, 6 packaging and the like. When the high-content manganese additive is dissolved into molten aluminum, the melting temperature is low, the melting time is short, and the recovery rate of manganese is high.