Blockchain applications, especially DeFi, frequently require off-chain data through oracles. Distributed oracles have higher security, but the system is also more complex. This paper designs a unified formal description method for the communication process, security protocol, data aggregation and other related procedures and protocols of the oracle. This method has no ambiguity and has a high logical description ability. Therefore, it has good convertibility with Event-B and some other formal verification tools, as well as logic methods such as first-order logic, set theory, and CTL, which can provide a basis for technical personnel to establish formal models, protocol development, and implementation. The paper defines and analyzes this protocol description method and presents examples of some core protocols.