The variability in the content of environmental isotopes 2H and 18O in precipitation over time is applied to study the characteristics of rainwater and the time-varying process in the atmospheric water cycle and the variable processes in the hydrological cycle. 26 rainwater samples were collected according to rainy days from August 3 to October 29, 2020 in Ha Noi. The stable isotope composition in rainwater ranged from -108.04‰ to -40‰ and -15.87‰ to -6.53‰ for 2H and 18O, respectively. Besides, the values of 2H and 18O were located around the local meteorological waterline. The stable isotope values also clearly reflect the correlation with the daily rainfall as well as clearly reflect the influence of season and ambient temperature on the change of stable isotope value with rainwater.