Product design must satisfy the requirement of product performance.Assembly tolerance is one of important factors relative to product performance.So there is a function relationship between assembly tolerance and product performance.This paper presents a self-adapting analysis approach matching assembly tolerance and product performance.The first is obtaining statistical data by experiments.We design two experiments including a part and a component of a complex mechanical product.We obtain twenty groups of data describing the relationship between tolerance and performance from the two experiments.The second is firing the twenty groups of data into mathematical relationship between tolerance and performance based on the Least Square approach.The third is to build the mathematical model between tolerance and performance by the generalization of the mathematical relationship hereinbefore.In the mathematical model,we can define the parameters of model to satisfy the different objects.So the self-adapting is achieved.Finally,we apply the approach successfully to analyze the relationship between assembly tolerance and product performance on a component of a complex mechanical product.