P2P is a largescale distributed computing protocol based on the Internet. It is useful to optimize and improve the P2P protocol by analyzing its basic principles with formal methods. The paper analyses the chord protocol with Abstract State Machine (ASM) and uses the Asml language to build the ASM model. The paper also designs the core running rules of Chord and computes the finite state machine (FSM) of Chord. This work can help to analyze and optimize the P2P protocol.