The preparation of dialkyl diselenides by the reaction of tosylates with disodium diselenide derived from hydrazine reduction of selenium promoted by sodium hydroxide needs high temperature (100 ℃), and this method is only suitable for preparation of the diselenides without functional group.Cesium ion (Cs+) is bulky, and the electrostatic interaction between cesium ion (Cs+) and anion is very weak.So the anion attached to Cs+ has strong alkality and nucleophilicity.The reaction proceeds more readily under mild reactive conditions using alkali of cesium as a catalyst because of the remarkable decline in activation energy.However, CsOH is very expensive compared to KOH. In this paper, according to the principle of ion exchange, using cesium chloride (CsCl) and TBAI as catalysts and dry DMF as solvent, hydrazine reduced selenium promoted by potassium hydroxide, followed by treatment with functional alkyl halide or tosylates at room temperature to afford corresponding diaryl diselenides in high yields.The method not only prepares diselenides containing functional group but has the advantages of mild conditions and high yields.