Abstract: The Longhua Ni-Co deposit in Jinxiu County is a hydrothermal Ni-Co deposit that has attracted considerable attention in recent years. There are seldom detailed reports on its formation process, especially on the origin and evolution of the ore-forming fluids. The ore-forming process in the Longhua deposit can be divided into at least three stages, aka quartz - nickeline - gersdorffite stage, quartz - gersdorffite stage, quartz - pentlandite - pyrite stage, the fluid inclusions in the associated transparent mineral quartz representing each mineralization stage have been observed by petrography and micro thermometry. The fluid homogenization temperature during the early mineralization stage of the Longhua Ni-Co deposit is 121~235 ℃, with salinity mainly ranging from 7.86 wt% NaCl to 35.87 wt% NaCl. The homogenization temperature during the main mineralization stage is 135~223 ℃, with salinity mainly ranging from 13.77 wt% NaCl to 35.87 wt% NaCl. The homogenization temperature during the late mineralization stage is 96~180℃, and the salinity is 3.21~26.64 wt% NaCl. The ore-forming fluid shows the characteristics of low to medium temperature and medium to high salinity. Combined with the hydrogen and oxygen isotope characteristics, it could be indicated that the ore-forming fluid is mainly derived from the ore-bearing hot brine that evolved from atmospheric precipitation that circulates and extracts the ore-forming materials from the Ni-rich strata, mixed with a small amount of magma and atmospheric water, and the fluid mixing and fluid cooling are the important factors leading to the precipitation of Ni-Co minerals in the deposit. The Jinxiu Ni-Co deposit belongs to a new type of hydrothermal filling deposit with low to medium temperature and high salinity.