The invention belongs to the technical field of volume dynamic measurement and discloses a volume dynamic measuring device based on laser scanning radars and a measuring method thereof. The volume dynamic measuring device based on the laser scanning radars comprises a conveying belt. A first laser scanning radar, a second laser scanning radar and a third laser scanning radar are correspondingly installed at the upper side, the left side and the right side of the conveying belt and are in the same vertical plane. The first laser scanning radar faces a conveying belt plane vertically, and both the second laser scanning radar and the third laser scanning radar face the conveying belt plane horizontally. The rotating shaft of the driving motor of the conveying belt is fixedly equipped with an incremental rotary encoder. The first laser scanning radar, the second laser scanning radar and the third laser scanning radar are electrically connected with an industrial control machine through a switch. The incremental rotary encoder is electrically connected with the industrial control machine through a data collection card.