The depreciation of machinery and equipment of building construction, as an important factor, always plagues the development of their enterprises; How to extract depreciation effectively and reasonably for construction equipment is a problem faced by construction businesses. In this paper, the gray relational theory is used to analysis different depreciation programs by author, and then the author selects the best depreciation program from all programs. The time value of money, the service life span of machinery and equipment and other factors are considered in this paper. A theoretical basis is provided for the construction enterprise to extract depreciation fast and reasonably through analysis these factors. And then the feasibility of the method is verified through the example analysis.