The invention relates to an oil-based annular protecting fluid injection technology, and belongs to the technical field of oil-gas well safety protection. The technology comprises the steps that before oil-based annular protecting fluid is injected, cleaning fluid, alcohol and other treatment agents are injected for soaking and cleaning, and then residual water, sulphur-containing substances, microorganisms and the like in a shaft are removed; finally, the purpose of improving the oil-based annular protecting fluid anti-corrosion effect is achieved. According to the technology, various different treatment agents are injected into a tubular column in a segmental mode, all treatment agent dosage calculation formula and specific proportion of all treatment agent ingredients are designed, andthe technology has good technological feasibility, and is worthy of application and popularization.