In this paper, we applied bottom-up linear optimization modeling to analyze long-term national impacts of implementing energy efficiency measures on energy savings, CO2-emission reduction, production, and costs of steel making in China, India, and the U.S. We first established two base scenarios representing business-as-usual steel production for each country from 2010 to 2050; Base scenario (in which no efficiency measure is available) and Base-E scenario (in which efficiency measures are available), and model scenarios representing various emission-reduction targets that affects production, annual energy use and costs with the goal of cost minimization. A higher emission-reduction target generally induces larger structural changes and increased investments in nation-wide efficiency measures, in addition to autonomous improvement expected in the Base scenario. Given the same emission-reduction target compared to the base scenario, intensity of annual energy use and emissions exhibits declining trends in each country from year 2010 to 2050. While a higher emission-reduction target result in more energy reduction from the base scenario, such reduction can become more expensive to achieve. The results advance our understanding of long-term effects of national energy efficiency applications under different sets of emission-reduction targets for steel sectors in the three major economies, and provide useful implications for high impact strategies to manage production structures, production costs, energy use, and emission reduction in steel making.