The invention relates to a catalyst for preparing alpha-acetoxyacetone by hydroformylation of vinyl acetate, the catalyst is generated in situ by a rhodium precursor, a phosphine ligand and an alkali metal salt aid in the presence of a solvent, and in the presence of the solvent, the alkali metal salt modified phosphine ligand and the rhodium precursor are coordinated to form a rhodium-phosphine catalyst system. Aiming at the current situation that a traditional vinyl acetate hydroformylation catalyst does not have isomerization catalytic reaction activity and cannot directly synthesize alpha-acetoxyacetone, the catalyst provided by the invention is characterized in that an auxiliary alkali metal salt is introduced into a rhodium-phosphine complex catalyst system; the purpose of catalyzing the generation of the hydroformylation product 2-acetoxypropionaldehyde of vinyl acetate and rapidly carrying out isomerization reaction to synthesize alpha-acetoxyacetone is achieved.