The invention relates to an oil-based drilling fluid with a low oil/water ratio. The drilling fluid comprises an oil phase, a water phase, an emulsifier, a wetting agent, oleophilic colloid, a filtrate reducer, lime, and optionally selected weighting agent and is prepared by mixing the abovementioned components. The oil/water ratio of the drilling fluid is (60:40)-(75:25). The invention also relates to a preparation method of the drilling fluid. The drilling fluid has the characteristics of low oil/water ratio, high viscous shearing, strong salt carrying performance, good rheological property, good suspension stability, and low toxicity. The emulsion-breaking voltage of the drilling fluid can reach 500 V or more. The water loss is less than 3 mL under a high pressure at a high temperature. The lubricating performance is good. The drilling fluid is suitable for the special construction technology applied on a high-inclination directional well, a shale horizontal well, and various wells in complicated stratums.