The present invention discloses an ultra-high density oil-based drilling fluid and a preparation method thereof. Oil-based drilling fluids in the prior art have the problems of poor emulsion stability and rheology, and easily lead to well wall chipping and collapsing, and blocking, long drilling cycle and other complex situations can be caused. The ultra-high density oil-based drilling fluid has a density of 0.93g / cm<3> to 2.80g / cm<3>, and comprises base oil, an emulsifier, a wetting agent, a tackifier, a filtrate loss reducer, a shear strength improving agent, an alkalinity adjusting agent, an aqueous solution of calcium chloride, a blocking agent, a weighting agent and the like, a formula and the preparation method of the ultra-high density oil-based drilling fluid are improved. The ultra-high density oil-based drilling fluid has good emulsifying stability and rheology, as well as mud shale strong inhibition, has the characteristics of small dosages of a variety of treatment agents, low preparation cost, high emulsion-breaking voltage, good rheology, low fluid loss, resistance to water, soil and salt and water-based drilling fluid and strong cement paste pollution performance and the like, and can be used in special drilling work in ultra-high pressure oil and gas wells, shale gas wells and strong water sensitive formation extended reach wells, horizontal wells and the like.