Abstract: The karst caves in the red bed are mainly developed around the basin, where the ground is dominated by coarse-grained tuffaceous or calcareous clastic rocks. The mixed ground condition formed by the said stratum and the overlying water-rich loose soil layer may pose a significant risk to the construction of underground works.Through the analysis of a series of engineering accident cases and in combination with the characteristics of construction methods of underground engineering, such as pile foundations, foundation pits and bored tunnels, this paper systematically summarizes main underground engineering construction risks in the red bed with developed karst:water inrush and mud gushing, slurry leakage and mud pumping, as well as resultant ground surface collapse and structural damage etc., and establishes the risk models regarding various construction methods. On this basis, prevention countermeasures are put forward, such as comprehensive geological survey, pretreatment with grouting and filling, observational construction and design, as well as hydraulic balance device for emergency use.