The invention discloses a preparation method of a reduced coenzyme Q10 and relates to quinone compounds. The preparation method comprises that an oxidized coenzyme Q10 is dried and then is dissolved in an organic solvent; the solution is added with a reducing agent and the mixed solution undergoes a chemical reduction reaction; the reaction product is added with a decomposition solvent and the mixture undergoes a decomposition reaction; the reaction product is filtered so that the filtrate is obtained; the filtrate is subjected to crystallization and drying so that white crystals which are the reduced coenzyme Q10 containing a trace amount of the oxidized coenzyme Q10 are obtained. The reduction reaction occurs in an ether solvent system, is a homogeneous reaction, has high reaction efficiency and solves the existing reaction dynamic problems caused by a reduction reaction occurring in a heterogeneous system. Reduction reaction post-treatment processes are simple, aluminum alcoholate salts produced by the reaction and unreacted lithium aluminum hydride or its derivatives can be decomposed by a solvent such as water, and granular precipitate lithium metaaluminate can be separated easily so that environmental pollution is small. A mass ratio of the reduced coenzyme Q10 to the oxidized coenzyme Q10 in the finished product is greater than or equal to 95/5.