The invention relates to a method for preparing biapenem with high purity, which takes low-cost Raney N1 as catalyst, and comprises the steps of: leading the catalyst and H2 to have hydrogenation reaction in buffer solution or the mixed solution of the buffer solution and organic solvent, removing protecting group, and then collecting biapenem from the reaction product. The method has mild reaction condition, simple operation, no need of resin purification, high purity of the obtained product and low production cost, and is suitable for industrialized production.