Provided in the invention is a sound collecting device of a mobile phone. The device comprises a base plate, a head baffle plate, side baffle plates, and a support plate. Two side baffle plates are arranged; the bottom of one side baffle plate is connected with the base plate by a horizontal folding expansion plate and the side is connected with the side of the head baffle plate by a vertical folding expansion plate; and the bottom of the other side baffle plate is connected with the base plate and the side is connected with the side of the head baffle plate. Protruding edges are arranged at the tops of the side baffle plates; and thrust blocks are arranged at the rear end parts of the protruding edges. A barrier strip is arranged at one end, opposite to the head baffle plate, of the front side of the base plate. Besides, a plurality of support posts are arranged at the front side of the base plate; a shaft seat is arranged at the back of the base plate; and the support plate is pivoted to the shaft seat. When a mobile phone is inserted into the barrier strip, the mobile phone is fixed by the protruding edges of the side baffle plates and the support posts arranged at the base plate; with the thrust blocks arranged at the side baffle plates, the mobile phone can only be inserted at a certain distance; and a sound outlet is formed in the head baffle plate. With the sound collecting device, the sound from the loudspeaker of the back of the mobile phone can be transmitted to the front side of the mobile phone.