A video decoding method includes: determining a largest size of a coding unit and a smallest size of the coding unit by using information about the largest size of the coding unit and information about the smallest size of the coding unit, the information being obtained from a bitstream; obtaining, from the bitstream, information about a largest size of a block allowed to be ternary split and information about a smallest size of the block allowed to be ternary split, determining the largest size of the block allowed to be ternary split, determining the smallest size of the block allowed to be ternary split, determining whether to ternary split a current block, and decoding blocks generated by ternary splitting the current block.