A method of decoding a motion vector includes: determining at least one prediction motion vector (PMV) candidate block used to determine a PMV of a current block; determining an availability of a motion vector of the at least one PMV candidate block; when there is a PMV candidate block determined to be unavailable, determining the PMV of the current block by using a default motion vector (MV); and obtaining a motion vector of the current block based on the determined PMV.