Conventional synthetic polymer HPAM exhibit poor temperature and salt tolerance, being prone to degradation and viscosity loss under high-temperature and high-salinity conditions, with residual monomers posing environmental risks. Microbial polymers, on the other hand, face challenges such as molecular chain scission and flocculation in extreme reservoir environments, leading to viscosity loss and difficulty in meeting the requirements of high-temperature (≥80°C) and high-salinity (≥30,000 mg·L?1) reservoirs. To address the demands of harsh reservoir conditions, a novel microbial polymer FH has been developed, and its rheological properties as well as its application potential in high-temperature and high-salinity reservoir environments have been systematically studied.The rheological properties of FH polymers were investigated by rheometer using factors such as temperature, salinity, shear force and pH value. Meanwhile, the microscopic appearance characteristics of FH polymers under different mineralization conditions were observed by scanning electron microscopy, and the long-term thermal stability and oil displacement effect of FH polymer in extreme reservoir environments were evaluated.The experimental results showed that both the novel biopolymer FH and xanthan gum have significant shear thinning properties. When the shear force was removed, the viscosity was reversible. But the viscosity of HPAM showed shear loss irreversibly. In the range of temperature (25℃~100℃), salinity (1000 mg·L?1~80000 mg·L?1 and pH (pH2.0 ~ 12.0), the viscosity of the novel microbial polymer remained unchanged basically. Especially in the high salinity of formation water, the novel biopolymer can form dense network structure, which enhances its harsh environmental tolerance. In addition, Under the treatment of high temperature and high salt for 40 days, the addition of sulfur-containing organic compound antioxidant could improve the thermal stability of biopolymer KF, and the adhesion rate reached 73.6%. It also demonstrated excellent oil displacement performance in physical simulation oil displacement experiments, increasing the crude oil displacement efficiency by 13.2%.