The invention discloses a preparation method of acid-modified superfine shell powder. The preparation method is characterized by comprising the following steps: 1) removing the cuticle of a shell raw material, and then adding water accounting for 20-80% of the weight of the shell subjected to cuticle removal, and stirring for 6 to 48 h to prepare slurry; 2), adding acid liquor accounting for 5-25% of the weight of the shell subjected to cuticle removal in the slurry, and stirring to obtain acid-modified shell micro powder slurry; 3), carrying out washing, filter pressing, drying and grinding on the acid-modified shell micro powder slurry to obtain modified shell powder with the particle size of 0.5-5 microns; and 4), adding purified water in the modified shell powder obtained from the steps 3), mixing into paste, and then adopting a planetary ball milling and grinding method to process, dry and crush to obtain the superfine shell powder with the particle size of 0.01-5 microns. The invention further discloses acid-modified superfine shell powder prepared by the method. The preparation method and the product are simple in process, small in equipment investment and low in energy consumption. Besides, the prepared modified shell micro powder is good in surface activity.