Although there are several special features in block-chain technology such as machine trust, traceability, and security, high energy consumption remains an issue in broadening the applications of block-chain technology. Some researchers proposed the use of proof of stake (PoS) mechanism rather than proof of work (PoW) mechanism to reduce energy consumption of block-chain. However, because PoS cannot guarantee fairness, mixed consensus mechanisms could be a solution and has been adopted in many studies. This paper aims to evaluate the performances of PoW, PoS and mixed consensus mechanisms from three aspects: energy consumption, fairness, and reliability. An agent-based model of a typical block-chain system equipped with different consensus mechanisms is created in NetLogo. This model simulates and evaluates the performances of different consensus mechanisms in the block-chain system.