The invention relates to a yellowish-brown humic acid-containing water-soluble fertilizer and a preparation method thereof. The preparation method comprises the following steps of 1, raw material quantitative proportioning, 2, reaction, 3, assistant addition, 4, stirring, 5, reaction, 6, cooling, and 7, packaging. The yellowish-brown humic acid-containing water-soluble fertilizer has total humic acid content greater than or equal to 40g/L, total nitrogen content greater than or equal to 80g/L, phosphoric pentoxide content greater than or equal to 40g/L, potassium oxide content greater than or equal to 80g/L, total trace element content greater than or equal to 60g/L, and water-insoluble substance content less than or equal to 50g/L. Potassium yellowish-brown humate, and macroelements and trace element necessary for plant growth are prepared into the yellowish-brown humic acid-containing water-soluble fertilizer. The yellowish-brown humic acid-containing water-soluble fertilizer has the advantages of high activity, comprehensive and balanced nutrition, high utilization rate, high hard water resistance, no flocculation, no deposition, and spray and drop irrigation adaptability. The yellowish-brown humic acid-containing water-soluble fertilizer can be widely used for a plurality of crops and can be directly sprayed on crop blade faces or punched and dropped on crop roots.