The oil-based drilling fluid with same water activity（0.9），density（ρ=1.8 g/cm³）and oil-water volume ratio（80∶20）composed by different internal salt such as CaCl₂，HCOOK，HCOONa and ₄Ca(NO₃)₃ was formulated indoors. The rheological property，dynamic/static settling stability，viscoelastic property and thixotropic ability of four different systems were compared and the anti-pollution ability of ₄Ca(NO₃)₃ internal oil-based drilling fluid was studied. The results showed that after the systems were aged under the temperature of 150℃ for 16 h，₄Ca(NO₃)₃ drilling fluid had the lowest shear force under the same shear rate compared with other drilling fluids with the lowest viscosity. The density decrease of ₄Ca(NO₃)₃ drilling fluid was only 0.255 g/cm³，while the ⊿ρ of other internal salt drilling fluids were 0.513—0.545 g/cm³ under the shear rate of 170.3 s^-1 at 50℃. The ratio of elastic modulus and viscosity modulus（G' /G' ）of ₄Ca(NO₃)₃drilling fluid was the highest among four systems，which showed that it had the best dynamic settling stability. When four drilling fluids were aged at 50℃ for 16 h after they were sheared under the shear rate of 10000 r/min for 30 min at 50℃，the surface tension of ₄Ca(NO₃)₃ drilling fluid was 27.744 mN/m²，the free oil volume was the smallest with only 1.37 mL and the density difference of upper and lower for the residual solution was only 0.038 g/cm³. It could formed the strongest gel structure with the peak of gel was 3.47 Pa. ₄Ca(NO₃)₃drilling fluid had the best static settling stability and thixotropic ability. 10% drilling solids and 15% salt water were added to the system to test the effect of drill solids and brine on the property. The result showed that₄Ca(NO₃)₃ drilling fluid had good anti-pollution performance.