The invention belongs to the field of drug synthesis and research, and particularly relates to an isomerization catalyst which is a palladium-carbon composite catalyst and is a mixture of palladium-carbon and triphenylphosphine, and the molar ratio of the palladium-carbon to the triphenylphosphine is 1 to (1-10). The invention further provides a novel isomerization method of acitretin. The isomerization catalyst is adopted to perform an isomerization reaction, so that an isomer 11-cis,13-trans-acitretin in the mixture can be effectively converted into a medicinal all-trans acitretin, materialwaste is avoided, the prepared acitretin product is high in purity, the palladium-carbon catalyst can be recovered by adopting a simple method and can be reused, the product cost is reduced, the concentration of heavy metal ions in wastewater is low, the environmental pollution is reduced, and the process is environmentally friendly.