在电力市场环境下，传统的发电计划转变为购电计划，其内涵发生了质的变化，购电计划的公平性和最优性是建立电力市场的前提。文中结合我国的实际情况，建立了以电网为核心的买电型短期交易计划的模型，提出了兼顾电网交易中心与发电商之间利益合理分配的浮动边际电价的新概念，并从电厂的角度给出了短期交易计划的公平性准则，从电网交易中心的角度给出了最优性判定准则。算例表明，根据该模型及其算法制订出的开停机计划和功率分配，能够体现电力市场的公平、公正、公开原则。 In the electricity market environment, the traditional power generation plan is transformed into a power purchase plan, and its connotation has undergone qualitative changes. The fairness and optimality of the power purchase plan are the prerequisites for establishing the power market. Combining the actual situation in China, the paper established a model of buy-and-buy short-term trading plan with power grid as the core, and proposed a new concept of floating marginal price that takes into account the reasonable distribution of interests between the grid trading center and generators, and from the perspective of the power plant. The fairness criteria of the short-term trading plan are given, and the optimality criterion is given from the perspective of the grid trading center. Examples show that the open and shut down plans and power allocations formulated according to the model and its algorithms can reflect the fairness, fairness and openness of the electricity market.