The invention relates to an electric power clearing decomposition method and system for a cross-regional dispatching electric power spot market, and the method comprises the steps: carrying out the clearing decomposition of the transaction electric power of a dispatching region based on the pre-obtained effective declaration electric power and electricity price; determining the total transaction amount of the power plant in the dispatching area according to the transaction power of the power plant in each clearing stage obtained by clearing decomposition; wherein the clearing decomposition comprises bid quantity decomposition clearing in day-ahead bidding, day-ahead allowance decomposition clearing and intra-day spot decomposition clearing.