Abstract: Correlations between design parameters and design objectives,especially the changeable correlations,are complicated for the design models of complex products.Hence,this paper presents a novel simplification method of design models for complex products based on the changeable correlation analysis.Design variables are partitioned into strong correlative variables,weak correlative variables and changeable correlative variables according to sensitivity analysis and information entropy theory,and then the design model is decomposed into the hierarchical model after simplifying weak correlative variables.In each calculation step of the hierarchical model,correlation strengths of changeable correlation variables are calculated according to the changeable correlation matrix.For each changeable correlation variable,if its correlation strength is strong enough in a calculation step,it is calculated in this step.Otherwise it is simplified.The structure optimization of a heat exchanger is taken as an example to verify the effectiveness of the approach.