In order to promote the application of energy saving technology, it is necessary to evaluate the economy, especially the lowest cost control in the case of consumer acceptance. Therefore, this paper combines the analytic hierarchy process and the data envelopment analysis (AHP-DEA), which evaluates the economy of energy saving technology application. It takes the use of solar water heater as a case study to verify the proposed model. In this paper, there are three important conclusions. Firstly, get the ideal control cost in the case of consumer satisfaction, through the application of AHP-DEA model. Secondly, it is necessary to promote the utility of renewable energy source. Thirdly, in order to promote the application of green building energy saving technology, cost should be considered and controlled. Finally, through analyzes the adjusted cost, initial cost and economic benefit, some references are provided for different decision makers.