The invention relates to the field of catalyst generation, and concretely relates to a cleaning solution used for an SCR catalyst, and an activity recovery method of a spent SCR catalyst. The cleaning solution used for the SCR catalyst contains fatty alcohol polyoxyethylene ether, sulfuric acid, ammonium sulfate and water, the content of fatty alcohol polyoxyethylene ether is 0.01-8 wt%, the total concentration of sulfuric acid and ammonium sulfate is 0.005-4 mol/L, and a molar ratio of sulfuric acid to ammonium sulfate is 1:(0.7-1.3) The cleaning solution used for the SCR catalyst can highly-efficiently clean away impurities in the catalyst. The activity recovery method of the spent SCR catalyst makes the activity of the SCR catalyst recover to be same or even better than that of the fresh SCR catalyst.