Complexity in chemical engineering design arises due to several reasons, e. g. heterogeneity of systems, multicomponent streams or complexity of performance measures for the system. This fact often leads to situations where multicriteria decision techniques are necessary or at least usefull. The authors demonstrate on an industrial example (design of a hydrocracking plant) how structural parameter approach in combination with multicriteria decision techniques can be applied to solve such problems and to perform a system analysis. The example makes obvious, how much more information can be obtained about performance of the system when multicriteria optimization rather than single criterion optimization is applied and how practical problems strongly demand for multicriteria techniques. To support the engineer during the design process a decision support system including an object oriented modelling tool, structural parameter optimization and multicriteria decision techniques has been developed at the BTU Cottbus. Structure and included functions of the tool are described and possible applications are outlined.