The Gaoshan Tunnel blasting vibration induced rockfall of a giant dry karst cave on QianjiangZhangjiajieChangde Highspeed Railway is dangerous and needs to be analyzed. As a result, the unmanned aerial vehicle detection, 3D laser scanning surveying and 3D laser scanner analysis are carried out. And then the blasting vibration monitoring system is established for dangerous rock of the karst cave by regarding the tunnel blasting vibration effect as the key item to acquire the blasting vibration velocity of the particle on karst cave surface. Finally, the calculation formula for blasting vibration velocity of rock of karst cave is given based on Sadaovsk formula; and the law of rockfall and the development rule of dangerous rock crack width are analyzed. Some main conclusions are drawn as follows: 1) The allowable blasting vibration velocity of giant karst cave rock is 1 cm/s; rockfall would occur when the particle vibration velocity exceeds 1 cm/s; and large volume rockfall would occurs when the particle vibration velocity exceeds 15 cm/s. 2) A full support system of steel tube column + Hshaped steel beam is used to guarantee the safety of the personnel and equipments during construction; and good effect has been achieved.