【英文摘要】The new technique for the determination of 18O/16O and 17O/16O isotopic ratios in water from small liquid sample has been set up in our study for the first time in China. The sample preparation system we devised is composed of two parts: one is the stainless steel system; the other is the vacuum system made of glass. The sample preparation process can be divided into four steps: helium carrier gas purification, micro-water sample introduction and fluoridation reaction, oxygen gas purification and cryo-focusing, oxygen gas transference and collection. The fluorination step takes less than 20 min, while the total processing time of each sample is about 40 min. We have optimized the method of water fluorination using the solid reagent CoF3 to produce O2, with 2μl micro water. Before isotopic determination we also heat up the molecular sieve to make the oxygen gas desorbed more perfectly and reduce fractionation effect. The new technique allows isotope ratio measurements by dual-inlet mass spectrometry with very high precision of ±0.07‰, ±0.14‰ and ±0.04‰ for δ17O, δ18O and △17O. In particular, the method does not use the fluorination reagent BrF5 employed in traditional methods, is hence safer, cheaper, higher efficiency and more reliable than traditional means and accords with the environmental awareness and the people-oriented principle. For so many advantages the new technique can be required in a number of fields, such as geology, hydrology, oceanography, and atmospheric sciences and so on. Based on the new system, we have determine tri-oxygen composition of many different type samples from different regions (the Heihe River Basin, the drought area in northwestern China, the Yangtse River and the Lhasa River), but there was no Δ17O anomalous values founded both in the precipitation samples and other typical samples like snow-water and so on. In spit of the regret results, we also make use of the oxygen-18 and hydrogen-2 isotopes to trace the origin, formation environment and transformation of nature water. During the period we carrying out the research, we have met amount of difficulties and also made cooperation with many environmental isotopic authorities home and abroad, then got a bit of great achievements.