Abstract: Aiming at the phenomenon of flowing sand in deep foundation pit engineering,we study the reason that the local instability of slope caused by quicksand and the measures to deal with it according to the concrete case of a deep foundation pit in Beijing.The study shows that there are a lot of factors which influence the flow sand phenomena,such as grain composition,structure,burial condition and quality problem of the process of construction.The first is blocking the seepage path of hydrodynamic pressure,such as waterproof curtain,steel sheet pile,gravel or pebbles after the wall and so on.The second is reducing the head difference of the inside and outside and the hydraulic slope,such as light well dewatering,waterway drain with draft tube.Through analyzing the concrete engineering case,it can solve the flow sand with adjusting measures to local conditions as well as learning for the similar project.