The invention discloses a preparation method of an emulsion. The emulsion is prepared by nanocrystallizing and hydrophobizing a wheat bran cellulose raw material, and taking the processed wheat bran cellulose raw material as a solid particle stabilizer. According to the method, nanoscale hydrophobized wheat bran cellulose is used as a solid particle stabilizer, the solid particle stabilizer possesses certain hydrophilicity and hydrophobicity, is capable of effectively preventing aggregation among liquid drops, and has a better stabilizing effect than common stabilizers; the Pickering emulsionprepared by the method provided by the invention is not layered after standing at room temperature for more than 30 days, and the ESI of the Pickering emulsion is 100% or close to 100%. In addition,the preparation method also has the advantages of low raw material cost, safe and non-toxic preparation process and environmental protection effect. Compared with a conventional acetylation method, anesterification method and a silanization method, reagents with obvious toxicity are prevented from being used, and the preparation process is safer and more environmentally friendly.