An expert system of regional crustal stability evaluation of the siting of key engineering works has been developed. It contains 610 rules and 200 statements. The system consists of eleven sub-knowledge bases that are organized into modes, so synthetic evaluation and individual assessment can be undertaken in order to suit various constructions and different evaluation levels. The structure matrix method is applied to combining various kinds of knowledge from such disciplines as geology, seismology and geophysics and to establishing the knowledge structure model from experts, which* provides a basic frame for the CRUSTAB system development. Knowledge representation of expert problem-solving is quantitatively illustrated by conventional experiment psychophysics. An assessment case of the application of the CRUSTAB expert system in the Guangdong Nuclear Power Plant is introduced.