Offline POS machine transaction method and system

The invention provides an offline POS machine transaction method, which comprises the following steps that an initialization process: key information, transaction data and user information are generated at each end and communicate with one another, and a mobile terminal calculates and generates a real private key du = r + k according to a private key factor r and a temporary private key k; a transaction process: the mobile terminal signs the transaction data T through a real private key du to generate a signature value S, and then generates a transaction two-dimensional code, wherein the POS machine scans a transaction two-dimensional code to obtain information, generates an abstract value e ''according to user information U, a public key Pca and a public key factor Pu, calculates and generates a real public key Qu = Pu + [e''] Pca, and uses the real public key Qu to verify a signature value S and process transaction data T. The method reduces information amount in a transaction process and can ensure transac