Aiming at the problem of frequent clogging of the injector in the calcium-based SDS dry desulphurisation system in the hot blast furnace flue gas of an iron and steel plant in Shaoguan, Guangdong Province, the causes of clogging were analysed and improvement measures were proposed by combining the high humidity climatic environment with the characteristics of the pipeline materials. The study shows that the clogging is mainly triggered by the high humidity of the conveying air (relative humidity ≥ 80%) and the roughness of the inner wall of the Q235-B carbon steel pipe (Ra = 6.3–12.5 μm): high humidity leads to the hygroscopic agglomeration of the calcium hydroxide, and the roughness of the wall exacerbates the retention of the powder and friction resistance (friction coefficient 0.3–0.4). By introducing a freeze dryer (handling air volume 7–10 Nm3/min, outlet humidity ≤ 30%) to dehydrate the conveying air in depth, optimising the pipe material to 304 stainless steel (Ra = 0.8–1.6 μm, friction coefficient 0.1–0.2), and replacing the single-venturi structure with an injector with an escape chamber, the frequency of system blockage has been reduced from 3–5 times per month to 0–1 times per month. After the improvement, the pressure fluctuation of the FGD system is reduced by 40%-50%, the maintenance cost is reduced by 30%-40%, and the flue gas emission indexes steadily reach the ultra-low emission standard of SO₂ ≤ 50 mg/Nm3 and particulate matter ≤ 10 mg/Nm3. This engineering practice provides technical reference for the optimisation of calcium-based dry FGD system in high humidity areas, with both environmental benefits and industrial demonstration significance.