Conventional synthetic polymer HPAM and xanthan gum exhibit poor temperature and salt tolerance，being prone to degradation and viscosity loss under high-temperature（≥80℃）and high-salinity（≥30 000 mg/L）conditions，and the residual monomer of HPAM is easy to pollute the environment，which is difficult to meet the development needs of high temperature and high salt reservoirs. To address the demands of harsh reservoir conditions，a new type of green and efficient microbial polymer FH had been developed. The effects of temperature，salinity，shear force and pH value on the rheological properties of FH polymer were investigated using a rheometer. The microstructure of FH polymer under different salinity was observed by scanning electron microscope，and the long-term thermal stability and oil displacement effect of FH polymer were evaluated. The experimental results showed that the viscosity of the FH solution，xanthan gum solution and polymer solution decreased sharply when they were sheared，and the higher the shear rate，the faster the viscosity decreased. When the shear force was eliminated，the viscosity of FH solution and xanthan gum solution became 109.3 mPa·s and 61.1 mPa·s，respectively，and the viscosity recovery rate was above 98%，indicating that the shear thinning phenomenon of the FH solution and xanthan gum solution was reversible and shear recovery was good. However，the viscosity of HPAM solution showed irreversible loss after shearing. Compared with xanthan gum，the FH polymer had a wide range of reservoir adaptability. The temperature resistance could be increased by more than 20 ℃，and the viscosity remained stable in both acidic and alkaline environments. Especially in the high salinity of formation water，the FH biopolymer could form a dense network structure，which enhanced 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 FH biopolymer，and the viscosity retention reached 73.6% . In the physical simulation oil displacement experiment，the injection of the FH polymer system（50 g/L FH +0.2% antioxidant S）enhanced the oil recovery by 22 percentage points based on water flooding（oil recovery being about 44%），which demonstrated superior oil displacement performance and had broad application prospects under extreme reservoir conditions.