Atmospheric peroxy radicals (RO2) are key intermediate radicals in the atmosphere, which occupy an important position in the tropospheric photochemical reaction processes. However, they are difficult to be measured because of their low concentration and high reactivity in the atmosphere. Chemical amplification, an indirect measurement technique, is one of the most commonly used methods of RO2 measurements. RO2 radicals are converted and amplified into high concentrations of stable NO2 via chain reactions by adding excess amount of CO and NO gas. Then the measurement of RO2 radicals could be achieved by measuring NO2 through different methods that are well developed. Chemical amplification is summarized, and different measurement methods of NO2 with their advantages and disadvantages are emphatically compared and analyzed. Finally, the directions for future research are prospected.