A continuous preparation method of a biodegradable aliphatic/aromatic polyester copolymer includes: performing a first esterification reaction of an aliphatic dihydroxy compound with an aliphatic dicarboxylic acid at a temperature of 185° C. or less; continuously performing a second esterification reaction of a reaction product from the first esterification reaction; continuously performing a first polycondensation reaction of a reaction product from the second esterification reaction to obtain a prepolymer; continuously performing a second polycondensation reaction of the prepolymer to obtain a second polycondensation reaction product having a melting index from about 15 g/10 min to about 25 g/10 min; and continuously performing a third polycondensation reaction of the second polycondensation reaction product to prepare the biodegradable aliphatic/aromatic polyester copolymer, wherein the performing of the first esterification reaction or the continuously performing of the second esterification reaction includes adding an aromatic carboxylic acid.