An ultrathin speaker module, comprising: a casing provided with a sound hole thereon; a speaker unit comprising a diaphragm; a first separating wall provided with a diaphragm accommodating hole, wherein the diaphragm is fixed in the diaphragm accommodating hole, and the first separating wall and the diaphragm separate the internal space of the casing into an upper space and a lower space; and a second separating wall, which separates the upper space into one first upper cavity and at least one second upper cavity, wherein the first upper cavity comprises the diaphragm and forms a front acoustic cavity, and the front acoustic cavity is in communication with the outside through the sound hole on the casing; and the at least one second upper cavity is in communication with the lower space through a through hole on the first separating wall, and forms a rear acoustic cavity.