Abstract: In the past twenty years, a continuous supervision monitoring of environmental radioactivity level around Qinshan NPP (QNPP) Base was carried out by Zhejiang Province Radiation Environmental Monitoring Center. The monitoring results show that the γ radiation dose rate around QNPP Base, the activity concentration of gross α, gross β, ⁴⁰K, and ¹³⁷Cs in aerosol samples, the gross β daily settlement in fallout, the activity concentration of ¹⁴CO₂ in air, the activity concentration of gross α, gross β, ⁹⁰Sr, and ¹³⁷Cs in environmental freshwater (drinking water, lake water and well water), the average-specific activity of ²³⁸U, ²³²Th, ²²⁶Ra, and ¹³⁷Cs in soils, and the average specific activity of ⁴⁰K, ¹³⁷Cs, ⁹⁰Sr, and ¹⁴C in edible plants, are not abnormal. The radionuclide contents in those samples are of the same levels compared with the background values before the operation of QNPP Base and the monitored values of Hangzhou reference site. However, the activity concentrations of ³H in air, rain water, drinking water, pond water, sea water of discharge site, and terrestrial plants are higher than the monitored values of Hangzhou reference site, and in some medium the activity concentrations of ³H outclass that of background around QNPP Base. The results indicate that after 20 years operation of QNPP Base, especially after the third phase heavy water reactors operation commercially, the external environment around QNPP Base has been affected by ³H in radioactive effluent.