Abstract: Complex contradiction often occurs in handling engineering contradictions. However, its definition and formalized description have not been studied, which make intelligent processing impossible. In order to solve the problem, complex contradiction and some key terms such as contradictory information unit and contradictory information unit set are defined and clarified. Also, the methods and steps expressing information units of complex contradiction are given. The results can provide theoretical basis for the analysis and solution of complex contradiction in intelligent processing on engineering contradiction.

Key words: contradiction; complex contradiction; information unit