A polyester-type waterborne polyurethane (WPU) was synthesized with 2,4-tolylene diisocyanate (TDI), poly-1,4-butylene glycol adipate (PBA), and 2,2-bis-(hydroxylmethyl) propionic acid (DMPA). A series of compression-molded sheets coded as STPU were prepared by mixing thermoplastic starch (TPS) with the desired amount of WPU. The properties and structure of the sheets TPS, STPU, and WPU were investigated by tensile tests, wide X-ray diffraction patterns (WXRDPs), differential scanning calorimetry, infrared spectroscopy, ultraviolet spectroscopy, and scanning electron microscopy. The results showed that the tensile strength, breaking elongation, and water resistance of the STPU sheets were all higher than that of TPS, when the WPU content was in the range from 5 to 30 wt %. The STPU sheets were found to have higher crystallinity than WPU and amorphous TPS and slightly lower light transimitance than TPS, suggesting that partially recrystallized starch formed. The WPU plays an important role in the formation of new morphology and in the enhancement of the mechanical properties of the STPU sheet. The compression-molded STPU sheets provided a potential application in the field of biodegradable materials.