The invention relates to a magnesium alloy integrally cast sound box which comprises a sound box body (1), wherein, a high-frequency loudspeaker (10), a medium / low-frequency loudspeaker (11) and an electronic frequency divider (7) are installed in the sound box body (1), the sound box body (1) is connected with a wiring post (8) through a wire, and a sound absorption layer (9) is arranged on the inner wall of the sound box body (1). The sound box body (1) is a magnesium alloy integrally cast structure, and a high-frequency loudspeaker hole (3) is arranged at the upper part of the sound box body (1); a medium / low-frequency loudspeaker hole is arranged at the middle part of the sound box body (1); and a sound-wave reversed phase hole (5) is arranged at the lower part of the sound box body (1). The manufacturing method comprises the following steps: the magnesium alloy is melted in a smelting furnace in the air or under the protective atmosphere, and the casting core can adopt a wooden core, metal core, and the like, by various molding and casting processes such as sand casting, metal mold casting, and the like; the magnesium alloy adopted in the method comprises the following component of Mg-X alloy, wherein, X can be an element such as Ni, Zr, Al, Cu, and the like, and one or more of the elements can be adopted to be combined with Mg to form binary, ternary or polynary magnesium alloy; and the sound box is characterized in that the seamless sound box body can be conveniently in any shape and complex structure. The invention has the advantages of simple structural process, low manufacturing cost and good tone color.