Substantially enhancing carbon mitigation ambition is a crucial step towards achieving the Paris climate goal. Yet this attempt is hampered by poor knowledge on the net economic effect of mitigation for each emitter, by taking into account potential cost and benefit. Here we use a global economic model with regional and sectoral disaggregation details to assess the mitigation costs for 27 major emitting countries and regions, and further contrast the costs against the potential benefits of mitigation valued as avoided social cost of carbon. We find substantial variabilities across these emitters in both cost and benefit of mitigating each ton of carbon dioxide and, more importantly, a strong negative spatial correlation between cost and benefit. The relative suitability of carbon mitigation, defined as the ratio of normalized benefit to normalized cost, shows great spatial mismatch with the mitigation ambition of emitters indicated in their first intended nationally determined contributions. China is relatively suitable for domestic carbon mitigation and could largely enhance their mitigation ambition. The European Union, which is economically less suitable to reduce domestic emissions, could work with many developing countries which are more suitable but less capable to reduce emissions. Our work provides important information to improve concerted climate action and formulate more efficient mitigation strategy.