The invention discloses a deepwater constant-rheology oil base drilling fluid applicable for deep sea drilling. The deepwater constant-rheology oil base drilling fluid applicable for deep sea drilling comprises the following components in parts by weight: 70-100 parts of white oil, 0-30 parts of a calcium chloride aqueous solution, 1.5-5 parts of a fluid type conditioning agent, 1-4 parts of an emulsifying agent, 0.5-2.5 parts of a wetting agent, 1-3.5 parts of organic soil used for drilling fluid, 1.5-5 parts of a filtrate reducer, 0.2-0.6 parts of calcium oxide and 0-260 parts of a weighting agent. The fluid type conditioning agent is at least one of ethylene-propylene copolymer, polymethacrylate, trimeric acid, phenolic resin, copolymer generated from reaction of dimer acid, cholamine and polyethylene polyamine and copolymer generated from reaction of acrylamide, styrene and methacrylic acid. The movable shearing force and six-speed viscometer of the oil base drilling fluid is respectively less than 6 r/min and 3 r/min, and the 10-min static shearing force can be kept steady within 4-65 DEG C; constant eheology is realized in the temperature range of the barrel of the deepwater drilling, technical demands on sea deepwater drilling can be satisfied, requirements on base oil raw material are loose, and the cost is low.