A new energy intensity (EI) index for steel production—energy intensity at specific scrap ratio (EISR) index—is developed in this study to provide a method for analyzing the EI difference of steel production through a case-study analysis for China and Japan. The real cause of EI change of China’s key steel enterprises from 2006–2014 is also studied by using the EISR index. Result shows significant technology progress decreases the EI of China’s key steel enterprises by 16% from 2006 to 2014, but the final drop of comparable EI was only 12.3% due to the continued decreased scrap ratio (SR). From 2006 to 2014, the main cause of EI gap between China’s key steel enterprises and Japan’s steel industry changed from gap in technological level to difference in SR. In factor analysis that assumed Japanese share of electric arc furnace production (23.2%) and SR (33.3%) in 2014 in China, the EI of China’s key steel enterprises decreased to 612 kgce/t (kilogram standard coal/t) (primary energy consumption), which is almost same as Japan’s data. The key task of energy conservation in China’s key steel enterprises in the future should be changed from upgrading the technology level to increase the SR of steel production.