The invention belongs to the field of chemistry, and relates to a synthetic method of asymmetrical thioether. The synthetic method comprises the following steps of (a) under the condition of catalysis of tetrabutyl ammonium halide, enabling a structural compound as shown in a formula (I), a structural compound as shown in a formula (II) and sulfur oxonium salt to react in a solvent so as to obtain the asymmetrical thioether with a structure as shown in formula (III), wherein R1 is selected from phenyl, substituted phenyl, naphtyl, substituted naphtyl, thienyl, or substituted thienyl; R2 is selected from hydrogen, phenyl, substituted phenyl, naphtyl, substituted naphtyl, thienyl or substituted thienyl; or R1, R2 and C connected with R1 and R2 form fluorene or thioxanthene; R3 is selected from hydrogen or an alkyl group; R4 is selected from hydrogen, phenyl, substituted phenyl, naphtyl, substituted naphtyl, thienyl or substituted thienyl; R5 is selected from hydrogen; or R4, R5 and C connected with R4 and R5 form the fluorene or the thioxanthene; R6 is selected form the alkyl group or the substituted alkyl group; and X is selected from C1, Br or I.