Qualify Engineering(QE) is purposed for company profits. It is difficult to understand the literature of QE which is published in Korean. In this paper, we want to make easy understanding of the QE and to apply it to real fields. Though that Taguchi has contributed to QE is absolute, QE and Taguchi methods are not the same methods. In this paper, we are trying to show differences of those. QE methods also are developed from the design of experience, the design of parameter and the on-line control of production process. Nowadays, the main subject of QE are to determine control variables and noise variables.