Abstract: In the event tree analysis of large complex system, the fault tree model of correlative safety systems will be generally put together as a large non-coherent fault tree to be analyzed. This is known as the normal fault tree link method that needs vast computer resource and calculation time. A fault tree construction method for event tree sequence and consequence was developed based on Demorgan and boundary conditions. In the light of the different treatments of every function event in the event tree of this method, the calculation can be finished fast as much as possible while fulfill the demand of analysis. Coding of the event tree analysis module of RiskA, which was an integrated reliability and probabilistic safety analysis program developed by FDS Team, was finished and several practical cases were tested to prove its validity.