This paper established a multi-level extension model for function effects post-evaluation of substation construction project, the model not only reduces the influence of subjective factors on the evaluation results, but also can determines the key factors which affect the quality of the evaluation results and overall developing trend of the project and provides some suggestions for the project late operation. Taking into account the fact that the element of the judgment matrix formed by traditional AHP is a certain value and may lead to a big difference from the judgment matrix formed by the different group of experts, thus reduces the credibility of the evaluation results; In order to overcome the problem, this paper introduces the concept of interval number, the maximum and minimum of judgment matrix elements relative importance comparison are used as the upper and lower limits of interval number respectively. Interval number are used as the elements of judgment matrix to make the evaluation result more rational. At the end, a practical 220kV substation construction project is taken as an example to verify the validity and rationality of the established model.