[Objective] Organic pollutants, such as chlorinated hydrocarbons and BTEX, have a major threat to the groundwater quality in our country. Natural attenuation monitoring plays an important role in the remediation technologies of contamination sites. The study of natural attenuation monitoring will be conductive to promoting the development of contaminated site control and remediation. [Methods]In order to study the natural attenuation of 1,2,3-trichloropropane (TCP) and benzene in different aquifers groundwater, the 3-year monitoring data of TCP, benzene, oxidation reduction potential (ORP), nitrate (NO3-) and biodiversity in an organic contaminated site has been collected and analyzed. Natural attenuation capacity of the pollution source area of the site was calculated using first order decay dynamics equation. [Results]The results showed that the natural attenuation of TCP and benzene occurred in the aquifer, and ORP values of phreatic and confined aquifer groundwater were -225~-57 mV and -182~-3 mV, respectively, which meant medium-high reducing environment, and anaerobic biodegradation of organic pollutants could be happened. Moreover, the effect of micro-biological degradation was stronger in the pollution source area and phreatic aquifer groundwater than that in non-pollution source area and confined aquifer, and the degradation rates of TCP and benzene in the phreatic aquifer of MMW02 monitoring well were 80.00% and 77.88%, respectively. The attenuation rate of TCP and benzene were 0.0018 d-1 and 0.0016 d-1 in phreatic aquifer, and 0.001 d-1and 0.0015 d-1 in confined aquifer. [Conclusions] Natural attenuation by microorganisms exists obviously in the groundwater contaminated by organic pollutants, but the decay rate is lower. The remediation time of the site will be longer by natural attenuation simply. Therefore, the effective remediation system for organic contamination in the groundwater should be established by the combination of natural attenuation with other technologies.