The invention discloses a method for decoding a video using a quad tree, a coding device and a decoding device. The method for decoding the video using the quad tree comprises the steps of decoding integrated code block flag information in a transform unit; decoding a split information flag based on size information and the integrated code block flag information in the transform unit; decoding the code block flag information in the transform unit without decoding the split information flag information when transform coefficients are not present in the transform unit; and decoding the code block flag information in the transform unit when the transform unit is not additionally split based on the split information flag, wherein the integrated code block flag is decoded on the condition that the transform depth in the transform unit is 0.