The present invention provides a transistor acoustic sensing element, a preparation method thereof, an acoustic sensor and a portable device. The transistor acoustic sensing element comprises a gate, a gate insulation layer, a first pole, an active layer and a second pole which are all arranged on a substrate; the active layer is of a nanometer fine wire three-dimensional mesh structure; and the active layer generates vibration under the action of sound signals, so that the output current of the transistor acoustic sensing element changes correspondingly. According to the transistor acoustic sensing element, the active layer of the nanometer fine wire three-dimensional mesh structure is adopted, so that the detection of the sound signals can be realized; since the active layer of such kind structure can sense the weak vibration of acoustic waves sensitively, the active layer of such kind structure can improve the sensitivity of the transistor acoustic sensing element to the sound signals, and therefore, the sensing performance of the transistor acoustic sensing element to sound can be improved.