The invention discloses an asiatic acid tromethamine salt lipid nanoparticle preparation and a preparation method thereof. The preparation method includes the steps of (1), adding asiatic acid tromethamine salt and lipids into absolute ethyl alcohol for dissolution according to a mass ratio of 1:1-1:7 to serve as an oil phase, wherein the lipids refer to solid lipids or mixed lipids of the solid lipids and liquid lipids; (2), dissolving surfactants into water to serve as a water phase; (3) dripping the oil phase into the water phase under stirring, and stirring till the absolute ethyl alcohol volatilizes completely, wherein the step (1) and the step (2) can be performed in any sequence. The asiatic acid tromethamine salt lipid nanoparticle preparation prepared by the preparation method is small in particle size of nanoparticles and high in encapsulation efficiency, drug loading capacity, stability and safety. The preparation method is simple and feasible.