Abstract: 【Objective】 The study aimed to study of leaf physiological properties and characteristics of hydrogen and oxygen stable isotopes of different plants in karst areas under extreme drought conditions， so as to provide a theoretical basis to cope with climate change， rocky desertification for the sustainable development of ecosystem of karst area.【Method】 Under the extreme drought conditions of 2022， the Langshi Underground River Basin （non-karst upstream area） and the Mashanmiao Underground River Basin （wholly karst areas） in the core region of the Lijiang River Basin were selected as study areas. Using typical plants in these regions—Shatang mandarin， Osmanthus fragrans， Broussone-tia papyrifera， and Vitex negundo as study subjects， field monitoring was conducted on leaf physiological properties of different plants （net photosynthetic rate， transpiration rate， intercellular CO₂ concentration， and water use efficiency）. Liquid water isotope analyzer were used to assess characteristics of hydrogen and oxygen stable isotopes in plant leaf to discuss water use strategies of karst plants under extreme drought conditions.【Result】 The average net photosynthetic rate 11.27 μmol/（m²·s） and average water use efficiency （3.65 μmol/mmol） of four plant species in the Langshi Underground River Basin were higher than those in the Mashanmiao Underground River Basin； the average intercellular CO₂ concentration in the Mashanmiao Underground River Basin （264.36 μmol/mol） was higher than that in the Langshi Underground River Basin； the spatial difference in transpiration rates of the four plants between the two river basins was relatively small. In the spatial distribution of hydrogen and oxygen stable isotopes in plant leaf water， the hydrogen and oxygen stable isotopes in leaf water of Osmanthus fragrans， Broussonetia papyrifera， and Vitex negundo in the Langshi Underground River Basin were higher than that of Mashanmiao Underground River Basin； the hydrogen stable isotope （δ²H） in leaf water of Shatang mandarin was higher than that in the Langshi Underground River Basin compared to the Mashanmiao Underground River Basin， while the oxygen stable isotope （δ¹⁸O） exhibited the opposite spatial distribution pattern. The kinetic fractionation effects of hydrogen and oxygen stable isotopes of leaf water in four plants， ranked from strongest to weakest as follows： Shatang mandarin （0.89）， Vitex negundo （0.90）， Osmanthus fragrans （1.40）， and Broussonetia papyrifera （1.52）. The deuterium excess （d-excess）of different plants was negatively correlated with hydrogen and oxygen stable isotopes in leaf water.【Conclusion】 Under the extreme drought conditions， water use efficiency of plants in the Langshi Underground River Basin， and enrichment of hydrogen and oxygen stable isotopes in leaf water is more pronounced. The Shatang mandarin mainly relies on artificial water supply intervention and has a weak drought to-lerance. Osmanthus fragrans and Broussonetia papyrifera adapt well to drought through lower kinetic fractionation effects and higher water use efficiency. Vitex negundo adapts to drought environments through its lowest water use efficiency and hydrogen and oxygen stable isotopes， reflecting a stronger drought tolerance of the shrub in karst mountainous areas.