The goal of the blockchain consensus mechanism is to make all honest nodes save the same blockchain view, while satisfying two properties: one is consistency, all honest nodes save the same blockchain stock; The second is validity, the incremental information published by one honest node will eventually be recorded by all other honest nodes in their own blockchain. The adoption of different consensus mechanisms on blockchain will have different impacts on the overall performance of the system while satisfying the consistency and effectiveness. We can evaluate the technical level of each consensus mechanism from the following three dimensions: (1) security, whether it is able to resist attacks from participants with certain resources and influence; (2) Scalability, that is, the more nodes, the greater the ability of the whole system to process transactions; (3) The degree of distribution, namely the access threshold and rights of nodes. The consensus mechanism has a triadic paradox: scalability, distribution, and security cannot be achieved in a blockchain system, but at most can be achieved in a second place. Therefore, how to find the balance among the three questions is the key to design the next generation consensus mechanism.