With the rapid development of China's rail transit construction, there are more and more urban subways, and various engineering problems appear gradually in the construction process. Karst is relatively developed in southern China, which brings some engineering problems to the safety construction of rail transit. Karst treatment technology has become a research hotspot in recent years. In order to solve the engineering problems caused by the karst of Nanning Metro Line 4, the distribution law of karst is proved by means of geological survey. Based on the geological survey data, the karst development law of Nanning Metro Line 4 is analyzed. The physical and mechanical parameters of stratum and karst cave are determined by core drilling and laboratory test. Combined with the finite element software MIDAS, the karst development law of Nanning Metro Line 4 is analyzed GTS determines the safe distance between karst cave and subway station and shield tunnel, puts forward the treatment scope and measures of karst cave for rail transit in karst area, and core the treatment area of karst cave, and studies the treatment effect of karst cave through indoor test. The research results show that the karst of Nanning Metro Line 4 is generally moderately developed; the karst caves in the station area are basically distributed within 10m below the floor, and the karst caves in the shield tunnel area are basically located within 10m below the floor and below the floor. The results show that the plastic zone is different in different positions and sizes, the higher the cave height is, the larger the plastic zone is, and the greater the safety distance is needed. The grouting reinforcement scheme is reasonable, and the detection results verify its rationality. It can provide reference for the treatment of subway station and shield tunnel in karst area.