Provided is a system and method in which a heat amount to be supplied to a regeneration tower for regenerating an absorbent may be lowered in an acidic gas capturing system for capturing acidic gas such as carbon dioxide. According to the system and method of capturing acidic gas, heat generated in the system itself is used to reduce energy consumption. According to the system and method of the inventive concept, heat exchange is conducted between low-temperature separated water generated in a capturing process and high-temperature processing gas to thereby reduce a cooling capacity of a condenser when condensing the processing gas, and also, a reboiler heat duty may be lowered by introducing the low-temperature separated water in a preheated state into the regeneration tower. In addition, the low-temperature separated water is used also in cooling a washing tower and a dilute solution through a heat integration process with respect to condensed water generated from the process itself, and thus, reduction of energy consumption of an absorbent regeneration process may be facilitated.