The invention discloses an emulsion for treating onychomycosis and a preparation method of the emulsion for treating onychomycosis. The emulsion contains eucalyptus oil, curcuma zedoary oil, oleum fructus bruceae, eugenol, self-emulsifying hybrid emulsifier AC-402, olive emulsifying agent, urea, salicylic acid, camphor, borneol, CMC-Na (sodium carboxyl methyl cellulose), sodium alginate, azone, boric acid, glycerol, hydroxypropyl methyl cellulose, 1,2-propanediol, fennel, lightyellow sophora root and a 5% ethylparaben propanediol solution. The emulsion for treating onychomycosis, prepared by the preparation method, has the advantages that the emulsion is high in functionality and little in toxicity or irritation, wherein the oleum fructus bruceae is capable of inhibiting fungus reproduction and effectively stopping fungal infection, a lightyellow sophora root extracting solution has anti-inflammatory and antibacterial effects, and all ingredients in the formula complement one another; compared with traditional medicines, the emulsion is better in treatment effect, higher in permeability and capable of avoiding relapse more effectively, thereby being capable of fundamentally treating onychomycosis caused by various fungi.