When a tunnel or any other type of underground opening is excavated in a carbon?ate rock area,lots of hazards due to the existence of karst such as the outburst of karst wa?ter, quick inflow of sand,opening collapese^etc. may possibly be met.This paper describes an expert system developed on the basis of the experineces from Chinese experts in the field of karst sciences,with the prediction of this kind of hazards as its target. As a decision support system,the prediction system can provide policymakers with the information about those haz?ards they have to consider in the processes of site determination, design and construction of underground projects so that they can avoid faults as far as possible, save investments and complete the project punctually. This system has been primarily verified by experts. In addition to the applications in railway tunnel construction，it can also be applied to hydraulic structures or underground mining for karst hazard prediction.