1. A decoding method of a video, the method comprising: obtaining a split transformation flag used to determine a transformation unit for an inverse transformation process, from a bitstream; obtaining at least one transformation unit from a coding unit based on the split transformation flag; determining a context model for arithmetic decoding a transformation unit significant coefficient flag indicating whether a non-zero transformation coefficient exists in the transformation unit, based on a transformation depth of the transformation unit; and arithmetic decoding the transformation unit significant coefficient flag based on the determined context model, wherein the transformation depth of the transformation unit indicates a number of times the coding unit is split, and wherein the context model is determined according to whether a value of the transformation depth is equal to 0 or not.