［Objective］To address the shortcomings of poor water resistance，thermal stability， and insufficient adhesion to PLA substrate in waterborne polyurethane，and to expand its application potential in the packaging and printing industry.［Methods］ A PLA/polysiloxane composite self-crosslinking waterborne polyurethane dispersion（PWPU）was prepared using polylactic acid diol（PLA-1000/PLA-2000）and polydimethylsiloxane（PDMS-1000）as composite soft segments，combined with a bifunctional chain extender（DDA）and a chain terminator（HBT）. The influence of the PDMS-to-PLA ratio on the material properties was systematically studied. The material structure and thermalproperties were characterized by infrared spectroscopy（FT-IR）thermogravimetric analysis（TG），and differential scanning calorimetry（DSC）. The water contact angle，s，urface tension，water absorption rate， and tensile properties were tested，and the surface，water resistance，and mechanical properties were systematically analyzed.［Results］The introduction of PDMS significantly improved the flexibility ofthe material. The elongation at break of PWPU-2 reached 234. 86%，which was 99% higher than that of pure PLA-based PWPU-1. Meanwhile，the hydrophobic segments of PDMS were enriched on the membrane surface，forming a low surface energy hydrophobic layer，which reduced the water absorption rate of PWPU-3（PLA/PDMS blend） to 4. 54% and increase the water contact angle to 74. 32° .Thermal stability analysis showed that the initial thermal decomposition temperature of the materialslightly decreased after the introduction of PDMS. This was the result of the combined effect of PDMScontent and the molecular weight distribution of the PLA soft segment，but the main decompositiontemperature dominated by hard segments was not affected. In terms of interfacial performance，the interfacial tension of PWPU-3 on the PLA film treated with corona was only 0. 489 mN/m，the adhesion energy reached 69. 48 mJ/m2，and the spreading coefficient was greater than zero，indicating excellent adhesion and cohesive failure characteristics.［Conclusion］ The prepared composite waterborne polyurethane exhibit high flexibility，low water absorption，good thermal stability and strong adhesion to PLA films，making it a promising eco-friendly binder for PLA packaging inks.