The invention provides a synchronous event response method for a three-machine hot backup real-time system. The three-machine hot backup real-time system comprises three one machines which operate independently, the one machines are in regular communication and exchange data in each control period, and each one machine in each control period comprises the following operating steps that S1, whether an event needing to be processed exists or not is inquired; S2, when the event needing to be processed arrives, the event state of the one machine is recorded; S3, the information exchanged between the one machine and other one machines after the event state is recorded, and whether other one machines are in an event state or not is inquired; S4, execution selection is carried out, wherein S41, if it is inquired that the three one machines are all in the event state in the step S3, response begins, or S42, if it is inquired that certain one machines are not in the event state in the step S3, a control period is awaited. According to the method, through information exchange between the one machines, whether data information is used or not is determined according to the received event state, one control period is awaited when the information is not synchronous, and the reliability and the completeness of the hot backup system are improved.