Provided is a method of continuous preparation of a biodegradable aliphatic/aromatic polyester copolymer, the method including: performing a first esterification reaction of an aliphatic dihydroxy compound and an aliphatic dicarboxylic acid at a temperature of 185° C. or less; continuously performing a second esterification reaction of a reaction product obtained by the first esterification reaction; obtaining a pre-polymer by continuously performing a first polycondensation reaction of a reaction product obtained by the second esterification reaction; and continuously performing polycondensation reaction of the pre-polymer, wherein an aromatic carboxylic acid is added to a reactor in which the first esterification reaction or the second esterification reaction is performed, to prepare the biodegradable aliphatic/aromatic polyester copolymer. According to the method of continuous preparation of the biodegradable aliphatic/aromatic polyester copolymer as described above, the amount of the aliphatic dihydroxy compound used, which is a starting material, is reduced and accordingly, manufacturing costs are reduced.