1. A decoding method of a video, the method comprising: obtaining a split transformation flag for a current depth, from a bitstream; when the split transformation flag indicates a non-split for the current depth, determining that a transformation depth is equal to the current depth; determining a context increasement parameter for determining a context index based on whether the transformation depth is equal to a predetermined value without using a size of a transformation unit; obtaining a context model for a transformation unit significant coefficient flag among a plurality of context models using the context index obtained by adding the context increasement parameter and a context offset; arithmetic decoding the transformation unit significant coefficient flag based on the context model; and determining whether at least one non-zero transformation coefficient exists in the transformation unit of the transformation depth, based on the transformation unit significant flag, wherein, when the split transformation flag indicates a split for the current depth, a transformation unit of the current depth is split into one or more transformation units of a next depth, and a split transformation flag for the next depth is obtained from the bitstream.