The invention discloses a special fertilizer for potatoes applicable to acid soil. The special fertilizer for potatoes comprises 19-38 parts of modified silica sol coated composite fertilizer and 62-81 parts of uncoated compound fertilizer, wherein a coating material silica sol in the modified silica sol coated composite fertilizer accounts for 2-5% of the total weight of the composite fertilizer;and the coated composite fertilizer comprises the following raw materials: urea, potassium sulfate, sodium selenate and a granulating agent. The uncoated compound fertilizer comprises the following raw materials: urea, ammonium sulfate, monoammonium phosphate, potassium sulfate, calcium magnesium phosphate fertilizer, zinc sulfate heptahydrate, borax and biotechnology fulvic acid. Acid soil improvement measures are taken, modified silica sol coating sustained-release treatment is performed, and a reasonable formula is confirmed according to potato growth requirements and soil nutrient characteristics. Moreover, medium trace elements are added, and the selenium element is supplemented in a form of modified silica sol coating selenate. The fertilizer disclosed by the invention has the advantages of being capable of improving soil acidity, improving the fertilizer utilization ratio, improving the yield and quality of potatoes and increasing additional value of potato products, time-saving, labor-saving and the like.