The invention discloses a stable weakly acidic whitening agent composition and a preparation method thereof. The stable weakly acidic whitening agent composition comprises the following raw materialsin parts by weight: 5-10 parts of 3-o-ethyl ascorbyl ether, 3-6 parts of nicotinamide, 2-5 parts of alpha-arbutin, 1-3 parts of butanediol, 1-3 parts of an emulsifier, 0.5-2.0 parts of jojoba seed oil, 0.5-2.0 parts of meadowfoam seed oil, 0.5-2.0 parts of tocopheryl acetate, 0.1-0.5 part of carbomer, 0.1-0.5 part of triethanolamine, 0.01-0.05 part of citric acid and the balance of water, whereinall the raw materials are 100 parts. Intervention and damping are performed on the whole stages of the initial stage, the middle stage and the final stage of melanin formation respectively, besides, the preparation method further performs micro-emulsification wrapping on the four whitening components to improve the stability of the four whitening components, and in addition, by adjusting the pH value, the absorptivity of the whitening agent, the compatibility of the skin and the stability of the whitening agent are improved. Therefore, the whitening agent which inhibits tyrosinase activation in the initial stage, inhibits oxidative antagonism in the middle-stage conversion process and prevents melanin transportation in the final stage, and is high in comprehensive skin absorptivity and extremely high in stability is obtained.