In order to investigate the influence of saturation on mechanical properties and longitudinal wave velocity of karst limestone，the experiment to on the mechanical property and the elastic wave velocity of karst limestone under natural and saturated condition was conducted. The results are as follows: Saturation has a significant influence on the softening of uniaxial compressive strength，tensile strength and elastic modulus of karst limestone，and peak strain and poisson's ratio of saturated sample are larger than corresponding values of natural specimen on the whole.The longitudinal wave velocity of water-saturated sample is significantly higher than that under natural condition，and the uniaxial compressive strength and tensile strength of specimen under two condition have a significant linear relationship with elastic wave velocity. Based on the current studies，he results are used to assess the stability of rock pillar between tunnel and concealed karst cave with high pressurized water，and calculate the minimum anti-inrush thickness.