Based on hydrological and meteorological data, the composition of hydrogen and oxygen isotopes in precipitation, surface water, and stream water were investigated for three typhoon events in the flood period of 2015 in the Hemuqiao Watershed, and the δ²H-δ¹⁸O relationship in precipitation was studied. The results show that the composition of hydrogen and oxygen isotopes in precipitation exhibited significant temporal variation. With the increase of the duration of rainfall, the δ¹⁸O values of the incremental rainfall with the same volume and rainfall during the same period had a decreasing trend. Throughfall, rather than rainfall, enriched heavier isotopes because of the canopy storage and isotopic fractionation. Rainfall was the main supply source of stream water. The contents of heavy isotopes in stream water were more abundant than those in precipitation and surface runoff due to the evaporation of stream water.