A method and system for feeding liquefied carbon-dioxide gas into the ground, by which liquefied carbon-dioxide gas can be efficiently permeated and diffused in a deep aquifer. The disclosed method for feeding liquefied carbon-dioxide gas into the ground includes the following steps:using a pumping well to pump up water from a deep aquifer to aboveground; creating injection water; applying pulsatile hydraulic pressure to the injection water; feeding the injection water to which pulsatile hydraulic pressure has been applied into the deep aquifer via an injection well; feeding liquefied carbon-dioxide gas—while maintaining carbon-dioxide gas in a liquefied condition—from a storage tank into the injection well to a depth having such pressure and temperature in which the liquefied condition can be maintained; mixing the liquefied carbon-dioxide gas—in the form of fine droplets—with the injection water, thereby generating a mixture of those two liquids.