Energy Performance Contracting, a type of contractual arrangements between clients and Energy Service Companies, is nowadays a key vehicle to implement energy efficiency measures in existing buildings. As well-designed contracts contribute to establishing partnerships between clients and Energy Service Companies and to promoting the Energy Performance Contracting's further development, this work was aimed to figure out the optimal solutions of the contract terms under two typical business models (the Shared Savings Model and the Guaranteed Savings Model). Based on game-theoretical methods, the non-cooperative scenario was considered at first because both the client and the Energy Service Companies are self-profit-oriented. However, the non-cooperative contracts are not so efficient as they cannot bring the maximal project profit. Thus, the cooperative game models where the maximal project profits were allocated between the contract parties were set up. The differences between the non-cooperative and the cooperative scenarios and the impacts of the parameters in the models were also discussed. The frameworks presented possible solutions for the contract-design problem under the Energy Performance Contracting and instructed the contract parties to conclude the most proper contracts.