With the development of tunnels and underground engineering,the problem of karst disasters is worsening.The water inrush is one of the most serious geological disasters during the construction of karst tunnels.Water inrush is likely to cause delay of tunnel construction,equipment scrapping and casualties.A 3-D numerical model of tunnel with spherical water-filled karst cave is established to investigate the minimum safe thickness criterion of karst cave and tunnel.Through numerical calculation,the variation rule of surrounding rock information is revealed in the situation of tunnel excavation with water-filled karst cave.The minimum safe thickness of the tunnel and karst cave is calculated,and the criterion of the minimum safety thickness of the tunnel and karst cave was preliminary studied.The regression relationship of minimum safe thickness was established for overlying water-filling karst cave of tunnels.Based on the methods of theoretical analysis and numerical calculation,the result can be supposed to provide favorable application value for tunnel construction.