The invention relates to a data synchronization method of a dual-machine hot backup interlock system. The method comprises the steps as follows: 1, a primary interlock machine and a standby interlockmachine separately divide data needing to be hot backed up into a plurality of data units according to the scale of the system, and store initial values of all the data units after starting; 2, the primary interlock machine sends a data information synchronization request to the standby interlock machine, and waits for reply information of the standby interlock machine within unit time; 3, the standby interlock machine receives the data information synchronization request of the primary interlock machine and judges whether to be synchronized with the data of the primary interlock machine; if yes, the standby interlock machine replies with a response request and waits for a synchronization signal of the primary interlock machine, and if no, the standby interlock machine sends correspondingstate information to the primary interlock machine and requests for the corresponding synchronization data; and 4, the primary interlock machine sends the corresponding synchronization data to the standby interlock machine according to the type of the information replied by the standby interlock machine, the standby interlock machine performs data replacement after receiving the synchronization data, and thus synchronous communication is completed.