As an indispensable part of the electricity market architecture, the spot market is the key to the coordination of market transaction and system operation security. In this paper, two major models, the incremental optimization and integrated optimization model, are studied. The differences between the two models in the treatment of power grid constraints, transaction delivery mode,the priority level and optimization result are analyzed. Examples are presented to illustrate the differences of dispatching result and total generation cost with incremental optimization and integrated power optimization. For the typical international clearing mode of spot market, including the Bid/Offer based balanced market mechnism of the UK and the intergated power optimization mode of USA, comparisons are conducted. Finally, based on the comparison of incremental and integrated optimization, the paper puts forward suggestions for the development and construction of China’s power spot market.