Olefins are one of the most important platform chemicals. Developing coal-to-olefins (CTO) processes is regarded as one of promising alternatives to oil-to-olefins process. However, CTO suffers from high CO2 emission due to the high carbon contents of coal. In China, there is 7 x 10(10) m(3) coke-oven gas (COG) produced in coke plants annually. However, most of the hydrogen-rich COG is utilized as fuel or discharged directly into the air. Such situation is a waste of precious hydrogen resource and serious economic loss, which causes serious environmental pollution either. This paper proposes a novel co-feed process of COG assist CTO in which CH4 of COG reacts with CO2 in a Dry Methane Reforming unit to reduce emissions, while the Steam Methane Reforming unit produces H-2-rich syngas. H-2 of COG can adjust the H/C ratio of syngas. The analysis shows that the energy efficiency of the co-feed process increases about 10%, while at the same time, life cycle carbon footprint is reduced by around 85% in comparison to the conventional CTO process. The economic sustainability of the co-feed process will be reached when the carbon tax would be higher than 150 CNY/t CO2. (C) 2014 Elsevier Ltd. All rights reserved.