The invention discloses a waterproofing agent with long-lasting water resistance for walls. The waterproofing agent comprises the following components, in percentages by weight: 3%-5% of stearic acid,0.1%-0.3% of sodium carbonate, 0.7%-0.9% of potassium hydroxide, 25%-27% of ferric chloride, 22%-24% of calcium chloride, 2%-4% of ammonia water and 42%-44% of water. A processing technology comprises the following steps: preparing the raw materials, melting the raw materials, performing primary mixing on the raw materials, performing secondary mixing on the raw materials, and performing sievingto obtain the finished-product filtrate. According to the waterproofing agent for the walls provided by the invention, the stearic acid is added, so that the waterproofing agent has the advantages ofgood water resistance, long waterproof service life, low process difficulty and low costs; the alkali metal compound sodium carbonate is added, the compound has a plasticizing effect, so that a water-ash ratio can be reduced, water seepage channels can be cut off and reduced, compactness of mortar can be increased, and the mortar has a waterproof property; and the ferric chloride is added, oxidized iron sheets and powder are used as main raw materials, and the ferric chloride waterproofing agent has the functions of strengthening and early strengthening, can continuously improve the compressive strength of concrete and has relatively high impermeability in the early stage.