The invention relates to biodegradable regenerated polyester and a preparation method thereof. First polyester reclaimed materials and polyester low polymer melt react to obtain preliminary depolymerization melt, and then the preliminary depolymerization melt and ethylene glycol react to obtain deep depolymerization melt, the deep depolymerization melt and ethylene glycol steam perform convection flow to obtain low TVOC content polyester oligomer melt, aliphatic divalent polyether esterification product is prepared, the polyester oligomer melt and the aliphatic divalent polyether esterification product undergo pre-condensation reaction to obtain low TVOC content precondensible polyester melt, the precondensible polyester melt undergoes final polycondensation reaction to obtain low TVOC content regenerative polyester melt, and finally the low TVOC content regenerative polyester melt enters a melt cooling pelleting system to obtain the biodegradable regenerated polyester. The method is moderate in overall process flow length and process control difficulty and has high efficiency, and the content of TVOC and nonylphenol and an isomeride thereof in the finally made biodegradable regenerated polyester is low.