As the requirement of detection, qualitative detection can no longer fulfill the current needs. In the fields of disease diagnosis, food adulteration, and clinical medicine and the detection of pathogenic bacteria and viruses, quantitative detection is crucial. From early real-time quantitative PCR to digital PCR, quantification has progressed from relative to absolute, and the instrumentation is growing much more automated. No matter how developed qualitative detection becomes, the fluorescent probe and dye are the key factors in achieving quantification. Hence, in the development of quantitative detection, various probes and fluorescent dyes have been created to enhance the specificity, improve the detection limit, and decrease the background interference. This review mainly describes the basic principle of each commonly used quantitative method and the advantages and weaknesses.