ApPhysical sound amplifying device is disclosed. The device is applied to a mobile phone, the mobile phone is provided with a loudspeaker sounding hole; The physical sound amplification device also comprises a sound amplification sound box. the sound amplification box is also provided with an air cavity; the air cavity channel is divided into a sound inlet cavity channel and a sound outlet cavitychannel; The first end of the sound inlet cavity channel is a sound inlet, the sound inlet is tightly attached to a sound outlet hole of the loudspeaker, one end of the sound outlet cavity channel isconnected with the second end of the sound inlet cavity channel, the other end extends in the sound amplification box and penetrates through one outer wall of the sound amplification box, a sound outlet is formed in the penetrating position, a throat is formed between the first end and the second end of the sound inlet cavity channel, and the sound outlet is larger than the throat. The playing volume and the playing effect of the mobile phone loudspeaker can be effectively improved without power supply of a power supply.