Research on characterizing and optimizing heat-transfer capacity (UA), an important design parameter determining separation efficiency and energy consumption in heat-integrated air separation columns (HIASC), is presented. The mathematical mechanism model of HIASC is built first, then characteristics of UA are explored. It is discovered that on one hand increasing of UA will lead to higher compressor load and thus brings higher energy consumption; however on the other hand increasing of UA will benefit mass transfer and conversely reduces energy consumption. For this reason, the optimal design on UA makes available the maximum energy efficiency together with considerable savings of the equipment investment, which provides guidelines for further designing of HIASC. Furthermore, an optimal partially coupled structure of HIASC is developed to exploit energy saving potential by lowering minimum temperature difference. The obtained optimization results show that the optimal design of UA for a fully coupled HIASC has achieved a 41.5% reduction in energy consumption compared to conventional air separation columns (CASCs) and up to 46.9% energy reduction is achieved by applying the optimal partially coupled design.