Abstract: Safety critical system is different from the general system for its multi-state failure particularity. It also has high requirements for maintenance on the grounds of its high safety and high precision particularity. By analyzing the characteristics of safety critical system and comprehensively considering the various securities caused by different components failure modes and maintenance modes, the model of tri-state component failure and multi-state system failure is established. As there are work, safety and danger three states for each component, when taking into account the complexity of system architecture, the system state number increases dramatically with the increase of the component number. The same situation is in the study of ion channels in biology. Based on Ion-Channel theory of biology, the states of safety critical system presented in this paper are aggregated and some important system dispersion and reliability indicators are drawn. The established model has carried on a more careful division to the system failure and enhanced the analysis accuracy.