The invention discloses a polyester elastomer for blow molding and preparation method thereof, and the polyester elastomer comprises the following components by weight percent: 88.0-96.9% of thermoplastic polyester elastomer, 3.0-10.0% of polyester liquid crystal macromolecular compounds, and 0.1-2.0% of isocyanurate compounds. The preparation method comprises the following steps: obtaining thermoplastic polyester elastomers by esterification reaction or transesterification reaction and condensation polymerization; adding polyester liquid crystal macromolecular compound and isocyanurate compound for reaction; obtaining the product. According to the invention, thermoplastic polyester elastomers are added with polyester liquid crystal macromolecular compounds and isocyanurate compounds, and the melt index of the obtained polyester elastomer for blow molding is between 0.5-1.5, and the product has higher melt-strength with good appearance quality, easier processing process and excellent mechanical properties.