Energy shortage is exacerbated by energy wastage and low efficiency, so energy efficiency has become a popular research topic. However, in most studies, the inputs and outputs of energy efficiency are selected through qualitative analysis and literature review, the rationality is not convincing. In this paper, the inputs and outputs of energy efficiency are calculated by EVA (Economic Value Added method). Number of employees in energy industry, energy consumption amount and energy services amount are chosen as the inputs while CO2 emissions per capita and industrial profit amount are chosen as the outputs. DEA (Data Envelopment Analysis) and Malmquist index are applied to calculate the energy efficiencies of nine countries during 2008-2012. Each country has different reasons to explain the change of energy efficiency index and more flexible energy development plans should be implemented according to the changing reasons. Then the important influencing factors of energy efficiency are analyzed by Panel Regression Model. The results indicate that technology indices and management indices are the main factors of energy efficiency. Management indices' effect on energy efficiency index is occurred mainly through pure technical efficiency change index. Technology indices' effect on energy efficiency index is occurred mainly through technical progress change index. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.