The method of fault tree analysis is an efficient method for the reliability analysis of complex systems. For evaluating fault tree

first we ought to obtain its minimal cut sets by using a computer. There are many algorithms developed during the last ten years to deal with this problem. Their main goal is to obtain minimal cut sets as quickly as possible using the smallest amount of main core memory. But a lot of difficulties still exist. The method presented by this paper has thoroughly solved the problem of occupying too much memory space so that it is possible to evaluate a large and complex fault tree on a small computer.Having obtained the minimal cut sets

the next step is to calculate the failure probability. Improving and developing the methods of [5] and [7]

this paper presents a method called circular cut transformation which can more easily transform the structure function into exclusive S-O-P form

it also has solved the problem of calculating Boolean Algebra on a compu-!er. The problem of calculating the failure probability of a large and complex system has been solved efficiently.