Today, with the development of science and technology, new products are created quickly using numerical simulation technology. One of the effective numerical simulation methods is the Polynomial Chaos method. However, when calculating with this method, there will be errors. When we do not know the exact result, we cannot know whether this error is large or small. In this article, the author develops a method to help determine the error of the Polynomial Chaos method, from which the approximate result can be determined with the exact result