Three kinds of scale inhibitors WJ-1, TJ-302 and TS-6 were used to modify the medium and high density brine and calcium brine.The formulation was prepared and applied to evaluate the scale inhibition performance of formation water and reinjection water in Dagang Oilfield.The test results show that the two modified formulas of calcium halide+1%～3% WJ-1 + 0.2% sodium dodecyl sulfate and salt brine+1%～3% WJ-1+1%～3% TS-6 + 0.2% sodium dodecyl sulfate can make the formation water of 7000 mg / L NaHCO3and 500 mg / L Na2SO4free from scaling at 90℃, the calcium retention rate reaches 90.0%,and the recovery rate of formation permeability 89%.Therefore, the formula is suitable for the formation with high alkali and high salinity, which can solve the problem of scaling and plugging formation in brine well killing operation in Dagang Oilfield,and has certain guiding significance for other formations of the same nature.