The invention discloses a method for modifying the surface of nano calcium carbonate. The method comprises the steps that 1, lime milk is added to a bubbling carbonatation reaction kettle, mixed gas containing carbon dioxide is introduced to the reaction kettle for a carbonatation reaction, carbonatation is conducted till the pH is equal to 7.0, carbonatation is completed, and a nano calcium carbonate suspension solution is obtained; 2, a stabilizer is added to the nano calcium carbonate suspension solution, the temperature is controlled within 50-60 DEG C, and heat preservation is conducted for 20-30 min; 3, a fatty acid modifier is heated and melted in water, an emulsifier is added to the fatty acid modifier, stirring is conducted for 10-30 min, and a modifier emulsion is obtained; 4, the nano calcium carbonate suspension solution obtained in the second step is added to the modifier emulsion, stirring is conducted for 30-60 min, and then through filter-pressing dehydration, drying and smashing, a nano calcium carbonate product is obtained. The prepared nano calcium carbonate has the advantages of good dispersity and processability, low oil absorption value, high thixotropy and activation rate, good stability, pH value close to neutral and the like. The method is low in production cost and simple in technology, facilitates industrial production and has good economic, social and ecological benefits.