Quantitative analysis in analytical chemistry is divided into semi-,relative, and absolute analysis. An example of each analysis is pH test paper, internal standard, and standard addition, respectively. However, their definition and differences have not yet been explained to students sufficiently in classes as well as textbooks. Polymerase chain reaction (PCR) is a good demonstration of quantitative analysis because it covers all three methods of quantification listed above. For example, traditional PCR can perform semi quantification; real-time PCR includes both relative and absolute quantitation. Therefore, in this tutorial article, we take PCR as an example to explain the kinds of methods of quantification to students. The basic principle and theories of the three PCR techniques for quantification are demonstrated and derived in detail. This will help students obtain comprehensive knowledge of quantitative analysis by studying the theoretical principles of different PCR techniques and further understanding their applications by comparing the characteristics of semi-, relative, and absolute quantification. This report is an attempt to combine teaching of chemistry with biology and present theoretical principles in a new way, which will be a helpful complement to teaching theoretical concepts in analytical chemistry and biochemistry courses.