As one of the most important theorists on Media Studies，Friedrich A. Kittler is always very difficult to understand. The complexity of his theory lies in that on the one hand，it stemmed from different and complex theoretical resources；on the other hand，his theory has developed new braches in the different periods. This paper will try to briefly sort out the inner thought of Kittler’s theory and introduce the key ideas of every stage to readers to help them understand Kittler better.