Provided is a history based CU depth determining method. A history based CU depth determining method according to an exemplary embodiment of the present disclosure is a method for determining depths of a plurality of coding units (CU) included in each of a plurality of coding tree units (CTU) which configures a frame of a video, including: dividing a plurality of previous CTUs of a plurality of previous frames which are the same position as a current CTU of a current frame into a plurality of areas to generate depth history information including information of a CU depth for each of the plurality of areas; determining a plurality of depth candidates for a CU depth for each of the plurality of areas of the current CTU, based on the depth history information; and selecting an optimal CU depth among the plurality of depth candidates for each of the plurality of areas of the current CTU, through a rate-distortion cost (RD-cost) calculation.