In order to study the effect of blasting on the anchoring force of long anchor cable through the karst cave, numerical simulation method is used, relying on a subway station pit support project, respectively, to explore the location of the karst cave, the diameter of the karst cave and the modulus of elasticity of the karst cave filler on the anchoring force of the long anchor cable through the karst cave under the effect of blasting. The results show that when the anchor cable anchoring section through the length of the karst cave the longer or the smaller the modulus of elasticity of the karst cave filler, the smaller the loss of anchor cable anchoring force before and after blasting; when the core of the karst cave and the distance from the pile is 10m, the loss of anchor cable anchoring force is the smallest; when the diameter of the karst cave is 4.46m or the modulus of elasticity of the karst cave filler is 13.3MPa, the void effect of the cavity absorbs the blasting energy, and the anchor cable anchoring force will not be lost after the blast. not be lost.