Rule set is a commonly used structure in rule engine. As an unambiguous rule set, the execution result in any context should be independent from the rule execution sequence. This paper proposes the necessary conditions of primal rule set to be unambiguous. An unambiguity verification algorithm for general rule set is also proposed to improve the unambiguity checking efficiency based on condition expression structural information. Rule set execution efficiency is really dependent on rule execution sequence. This paper discuss how to reduce the times of condition checking by sorting rules according to rule execution trace. Two heuristic algorithms are proposed for the optimization problem. The efficiency of the algorithms is illustrated through a toy example. © 2010 IEEE.