An alkali washing liquid for regenerating SCR denitration catalysts and an application thereof are provided. The alkali washing liquid is composed of an organic alkali, a surfactant and deionized water, wherein the organic alkali is a mixture of one or two of ethanol amine, diethanol amine, triethanolamine, triethylamine and N-methyl diethanol amine. In the method for regenerating the SCR denitration catalysts, firstly, to-be-regenerated SCR denitration catalysts are subjected to air purging and cutting, then immersed in the alkali washing liquid, and subjected to ultrasonic alkali washing. Compared with the prior art, the method has surface repairing and surface reconstruction processes aiming at the to-be-regenerated SCR denitration catalysts increased, and finally, after active ingredient supplementing and calcination processes, the specific surface area and the denitration rate of the obtained regenerated SCR denitration catalysts are both relatively greatly improved compared with those of the conventional washing and regeneration technology. The alkali washing liquid is suitable for regeneration treatment of the honeycomb type, corrugated type and plate type SCR denitration catalysts.