Abstract: With the advancement of market reform, the number of subjects in the electricity retail market has increased significantly. However, this growth also leads to an escalation in disputes and claims between users and electricity trading companies, especially among small and medium-sized users who lack the awareness of market competition. This situation will directly affect the enthusiasm of users to participate in the market and hinder the promotion of the construction of a unified national electricity market. Therefore, it is imperative to assist these users in understanding the market price transmission mechanism and further improve the construction of the retail market. To this end, in this paper we study on the trading strategy for small and medium-sized users to participate in the retail market, enabling them to make more informed decisions on selecting the retail package suitable for their own load conditions. The research is based on the master-slave game. Firstly, an upper model is constructed with the maximization of the revenue from the sale of electricity by the electricity selling company as the optimization objective. Secondly, a lower model is established with the lowest cost-utility of the user as the optimization objective. The KKT conditions for the two-layer are adopted for solving the upper and lower iterations of the planning model. Finally, the model feasibility is verified through examples, and the reference prices for electricity are given for relevant retail packages under different business scenarios.