Abstract: With the continuous advancement of power system reform, as a new market entity, it is particularly important for electricity retailers to grasp the business opportunities accurately and understand market trading strategies clearly. Therefore, based on the medium-term and long-term electricity trading mechanism, by taking full account of the diversity of power market and trade, this paper introduces the contract transfer transaction and the energy deviation penalty assessment as the market power balance mechanism, then establishes the optimization decision model of electricity purchasing strategies for electricity retailers. Aiming at the maximization of the profit, a hybrid adaptive bacterial foraging method, i.e., particle swarm optimization algorithm (ABFO-PSO) is adopted to solve the problem. Finally, the validity of the model and method is verified through case studies. The study can provide the reference for electricity retailers to participate in market competition.