The invention discloses a tackifier for an oil-based drilling fluid. The tackifier is prepared from the following raw materials in parts by weight: 800-900 parts of bentonite, 130-170 parts of a modifier and 45-55 parts of white oil. The modifier is selected from cetyl amido propyl dimethyl dodecyl ammonium chloride, cetyl amido propyl dimethyl tetradecyl ammonium bromide, stearyl amido propyl dimethyl dodecyl ammonium chloride and the like. The preparation method comprises the following steps: allowing bentonite to pass a 200-mesh sieve, mixing the processed bentonite with the modifier, adding white oil, and uniformly mixing to obtain the tackifier. The tackifier is used in the oil-based drilling fluid; after the tackifier is added into the drilling fluid, the apparent viscosity, the plastic viscosity, the dynamic shear force and the like can be controlled; after the tackifier is added, the drilling fluid is high in viscosity, moderate in dynamic shear force and low in filtering vector, facilitates the stability of a well wall, and meanwhile, is resistant to high temperature, calcium, magnesium and salt.