Manufacturing water-stable carboxymethyl cellulose (CMC) films as an alternative to commercial plastics is a promising solution to address plastic pollution. In this study, waste walnut shell (WS) was used as a natural lignocellulosic filler, glycerol as a plasticizer, and citric acid (CA) as a crosslinking agent for preparing high-performance CMC-based bioplastics through a one-pot casting method. When WS content was 12 wt%, the obtained CWGA-12 after optimization exhibited excellent mechanical properties (tensile strength ≈18.53 MPa, fracture strain ≈78.11 %), low surface roughness (<
16 nm), high optical transmittance (82.23 %), and superior thermal stability. Moreover, CWGA-12 could not decompose within 7 days of immersion in water, or even after 5 h of continuous stirring at 60 °C, while it could be reused after crushing, dissolving, and re-pouring under alkaline conditions. The alkali-recycled CWGA-12 exhibited a better UV-blocking capacity than before (99.22 % for UVA and 99.95 % for UVB). In addition, our bioplastic also had excellent biodegradability and disappeared completely after 2 days in rainy weather. Thus, our work not only offers an innovative approach to producing petroleum-based plastic substitutes with outstanding water resistance and UV-blocking properties but also paves the way for WS waste's broader applications.