The flow of people changes very greatly in the public areas of public buildings, so the energy demand should also change with the flow of people. However, under the traditional model, the pedestrian flow is rarely considered when accounting energy output, which causes some of the energy invalid. How to assess the energy efficiency to reduce energy waste is an emergent problem to be solved for building energy conservation. The concept of energy utilization efficiency is put forward to judge the degree of utilization of energy, and the formula for calculating energy utilization efficiency is also provided. In a hospital public waiting area, a lot of experiments have been carried out. By comparing the energy consumption before and after the experiments, it is found that energy utilization efficiency can assess the effectiveness of energy. And to improve the energy efficiency of buildings greatly in public areas can be realized by promoting the energy utilization efficiency.