The impact of the change of oil/water ratio resulting from formation water invasion in the process of drilling on rheological property of drilling fluid is a topic which is well worth studying. This thesis employs M3600 automatic rheometer to measure the rheological parameters based on oil-water ratio (2:8/3:7/4:6/5:5/6:4/7:3/8:2) of oil base drilling fluid at different temperature (30℃, 60℃, 90℃) respectively. In these cases, The change of oil-water ratio in oil-base drilling fluid causes the change of rheological properties when water invasion happens. The experiment proves: oil-base drilling fluid belongs to the plastic fluid when the oil-water ratio is greater than 1; oil-base drilling fluid is more inclined to the pseudoplastic fluid when the oil-water ratio is less than 1. Under the same temperature, as the oil/water ratio decreases, The oil-base drilling fluid shear stress and viscosity as well as the static shear force all rise with the decrease of oil/water ratio. The higher temperature of the oil-base drilling fluid is, the smaller shear stress and viscosity as well as static shear stress will be under the same oil-water ratio . The demulsification voltage of oil-base drilling fluid will decrease as the decrease of oil/water ratio, that is to say the stability is becoming worse.