The researching of free radical is basilic researchful approach for free radical's chemistry, biochemistry and medical chemistry. Usually free radical has better activity and shorter half life, hence there have many methods for us to study free radical. In these methods, according to different apparatus, they can be seen as electron spin resonance, chemiluminescence, fluorescence, spectrophotometry, chromatography and radiolysis, etc. Because different apparatus has different detecting object, area and precision, each kind of methods has it's own specialty. Hence it is necessary for us to find and select a right way to study.