Story Parsing Grammar(abbr. SPG)based story understanding approach,proposed by the author, is a formal method orienting the deep level meaning of the story to understand the syntax, semantics and pragmatics of the story. SPG is highdimensional and context - sensitive. In order to strengthen SPG s descriptive ability and widen SPG s representative scope, a special kind of production, called unordered production, is defined and introduced into SPG. Concequentially, influences of unordered production on SPG are discussed.Moreover the charateristics of the unordered production in SPG are discussd.The syntactic parsing algorithm of a subclass of SPG with unordered productions is given at last.