Disclosed are a fluidized bed water gas shift membrane reactor and a method for separating carbon dioxide using the same. More specifically, disclosed are a fluidized bed water gas shift membrane reactor provided on the back of a gasification reactor to produce a synthetic gas consisting of hydrogen and carbon monoxide by reaction of a solid hydrocarbon with water or oxygen, wherein the carbon monoxide present in an amount of 40 to 70 vol % in the synthesis gas reacts with steam in the presence of a catalyst to produce a mix gas of hydrogen and carbon dioxide, and the hydrogen is selectively isolated from the mix gas through a Pb—Cu shift membrane to increase the concentration of carbon dioxide present in the mix gas and separate the carbon dioxide, and a method for separating carbon dioxide using the same.