Abstract: Use of isotope tracer technique of natural water can effectively trace water origin and transportation process, and reveal recharge and discharge relationship of various water bodies and hydraulic connection of various hydrogeologic units. It has important application values and is of scientific significance for protecting and developing the precious natural resources, and provides reference for the similar researches. The following results have been obtained in this research: (1) There is hydraulic connection between Zhanghai and the middle course of Rizegou. The water in Zhanghai leaks at Jianzhuhai-Tianehai area in Rizegou along the karst passages with the fault zones. The leakage water in the rainy season accounted for 21% of the total runoff volume in Jianzhuhai, and about 28% in the dry season. The absolute leakage water volume was stable and almost no change occurred with changes in seasons. (2) There are independent karst passages and groundwater reservoirs in areas from Wuhuahai to the middle upper courses of Zangmalongli in Rizegou. The rain water in the middle upper courses of Zangmalongli during the rainy season drained off through the independent karst passages. The outlets are located in areas between Wuhuahai and Xiongmaohai. The amount of water discharged into Wuhuahai accounted for about 30%. In the dry season the amount of water drained off into Wuhuahai in the same form dropped to the lowest point, but did not cause obvious influence on the amount of water in Wuhuahai. (3) Based on the runoff isotope composition features of Zhanghai and Rizegou, only part of the runoff in the highest concation of Zezhawagou source recharged into the downstream of Zhanghai, and the other part fell down to discharge into Zangmalongli valley of Rizegou source through the well developed karst passages along the NW fault zone. This is one of the important reasons accountable for the abundant runoff in Rizegou all the year round. (4) There is no direct hydaulic connection between Danzugou and Wuhuahai, and the water over the dry valley fell down to discharge through the subterranean karst passages, and the discharged mouth is at the downstream area in Wuhuahai.

Key words: Jiuzaigou, Isotope tracer, water cycle system