Atmospheric precipitation is the main input source of the water cycle system

and the stable isotope compositions (δD

δ

18

O

) are greatly influenced by regional meteorological and geographical factors and are very sensitive to environmental changes. Stable oxygen and hydrogen isotope technique is widely used to study the characteristics of the global and local water circulation. The Dongjiang River Basin is located in the Pearl River Delta

China. The monsoon circulation controls the time and space distributions of precipitation by affecting the distribution of water vapor transport field. The lower reaches of the Dongjiang River was taken as the research object to study the mechanism of regional precipitation. Daily precipitation samples were collected in 2017

δD and

δ

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O

were measured and the relationships between δD

δ

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O

and temperature

precipitation were analyzed. The HYSPLIT backward trajectory model was used to trace water vapor sources and the transport of regional precipitation. The results show that the δD and

δ

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O

values ranged from -105.10‰ to +9.98‰ and -14.80‰ to -0.55‰

respectively

and the annual weighted mean values were -57.88‰ and -8.61‰. Regional Meteoric Water Line was δD=8.60

δ

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O

+16.51(R

2

=0.99). The maximum

δ

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appeared in January

which was -3.47‰

and the minimum value appeared in August

which was -10.17‰. In the monthly scale

δ

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O

shows “anti-temperature effect” and “quantity effect” The δD and

δ

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O

in precipitation which caused by water vapor in the Pacific Ocean were higher than those in the Indian Ocean. However

the δD and

δ

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O

in precipitation caused by the air masses from the South China Sea changed with the seasons

which weres significantly lower in summer and autumn than those in spring. There was obvious circulation effect of isotope in atmospheric precipitation.