In the electricity retail market based on real-time pricing, the electricity price is highly volatile and uncertain. Customers need to adopt appropriate risk management tools to avoid or control risk. First, a flexible contract was proposed based on the idea of optional contract between an electricity retail company and a customer, in which the customer can set the strike price of the flexible contract as the highest market price it is willing to pay. The flexible contract can not only enable the customer to avoid the risk of adverse price fluctuations in the retail market, but also remain the opportunities for the customer to make profit when the market price fluctuates favorably. Second, in order to determine the risk premium of the flexible contract and encourage both parties to participate in the contract transaction, a utility function considering customer type was introduced to describe the electricity consumption willingness of different customers, and the upper limit of the premium was determined under the condition that the customer’s net utility with the flexible contract was not less than that without the contract. From the viewpoint of the retail company, a risk decision-making model considering the upper limit of the premium was also proposed to determine the premium. Finally, an example was given to verify the reasonableness and effectiveness of the proposed model.