Abstract: Based on the analysis of geologic background and rock fabric, the fluid inclusions in lacustrine hydrothermal sedimentary rock from the Xiagou Formation, Lower Cretaceous in Qingxi sag, Jiuquan basin is studied.The results show that, native fluid inclusions in hydrothermal sedimentary rock mainly include vapor-liquid types, in which they lack the haploid liquid and haploid vipor and triune inclusions of filial mineral are less.The mineralizing fluid is NaCl-H2O hydrothermal brine system.The temperature vary between 90℃ and 200℃, salinities between 8% and 22% NaCl eq., density between 0.99 g/cm3 and 1.2g/cm3 and mineralization pressure between 15Mpa and 180Mpa.Integrated with Sr isotope analysis, we think the mineralizing fluid is deep circular lake water with magma water, with low-mid temperature, mid-high salinity and mid-high density, and present that the temperature, salinity, density and pressure of the mineralizing hot fluid of hydrothermal sedimentary rocks contained different types of barite, ankerite and fluorite in different location decreases outwards by the order: main exhalative-channel—branch exhalative-channel—exhalative mouth—near exhalative mouth—distal basin.Based on the analysis of the characteristics of hot fluid, the mineralization mechanism of the Early Cretaceous sublacustrine hot fluid in the area is discussed.