The present invention relates to a method and system for treating a liquefied gas, which system includes: a liquefied gas supply line for connecting a liquefied gas storage tank and a user's place; a pump arranged in the liquefied gas supply line for pressurizing the liquefied gas discharged from the liquefied gas storage tank; a heat exchanger arranged between the user's place and the pump in the liquefied gas supply line for enabling the liquefied gas supplied from the pump to perform heat exchange with a heat transfer medium; a heater for heating the heat transfer medium; a heat transfer medium circulatory line connecting the heater and the heat exchanger; a heat requirement calculator for calculating a heat quantity required for the heat transfer medium based on a calculated flow rate of the liquefied gas supplied to the heat exchanger and the quantity of the liquefied gas demanded by the user's place; and a controller for varying the flow rate of the heat transfer medium coming into the heater or the heat quantity supplied by the heater to the heat transfer medium according to the heat quantity required for the heat transfer medium calculated by the heat requirement calculator.