Abstract: In order to study the concentrations, distributions and influence factors of radium and radon isotopes in underground water in the lower reaches of the Yellow River, we carried out five surveys along the lower reaches of the river channel from Lijin station to the Yellow River estuary in different seasons from May, 2015 to February, 2016. The results indicate that:① Concentrations of the three radium isotopes (²²³Ra, ²²⁴Ra and ²²⁶Ra) were 0.4~5.9 dpm/100L, 23.5~358.1 dpm/100L and 11.2~49.4 dpm/100L in underground water in lower reaches of Yellow River; The ²²²Rn contributions was 8.2~700.5 dpm/L, in addition to individual site (such as DP-# site), the ²²²Rn concentration was higher (608.8±105.0 dpm/L), the ²²²Rn concentrations ranged from 8 to 200 dpm/L in other sites. ② Far away from the Yellow River Estuary, radium isotopes did not have significant variation among seasons (LJ-#, YL-# and YW-#). In area close to the Yellow River Estuary (DP-# and KY-#), radium isotopes changed a lot among seasons. Along the direction to the Yellow River mouth, radium isotopes concentrations increased, and salinity was found to be the main controlling factor. ③ ²²²Rn concentration was higher in winter than summer, the groundwater residence time and river discharge amount were the main influence factors.