This paper details the design and implementation of an expert system fortrap evaluation, into which the users can input their information about a trap, Ittherefore provides the evaluation of oil and gas conditions of the trap accordingto the expert's knowledge already built in the system. By adopting the methodsof rule-based knowledge representation, deductive reasoning, fuzzy reasoning,fuzzy judgment and the blackborad-based control stucture, the system is imple-mented in msc 6.0 and some assemble language on the IBM-PC microcomputer. Ithas been authenticated by experts.