Abstract: A dual-computer parallel redundant structure of a micro-computerized automatic block system between railway stationswas designed tomeet the need forhigh reliability of railway signalling. The principle and behavior of safety control lock were discussed to avoid the state of dual-host- computer. The theory of Petri net was used to model and analyze the system to investigate its transforming performance. The analytical results show that the proposed structure and the transforming method are reasonable, the states in the system can be transformed safely and perfectly, and there isno a dead lock state.