Abstract: In order to reduce the "ghost fishing" and "white pollution" caused by lost fishing gear, the degradable fishing gear materials has become one of the effective ways to achieve sustainable development of China's fishery. In this study, polyadipic acid/butylene terephthalate (PBAT) monofilament and PBAT/starch composite monofilament were prepared by melt spinning, and the thermodynamics, mechanical properties, weight loss rate, infrared spectrum and microstructure changes of PBAT fiber and PBAT/starch composite monofilament that were degraded for 5 months under different artificial seawater degradation environments were compared and analyzed, and the effects of temperature and pH on the seawater degradation performance of the two monofilaments were studied. The results showed that the inclusion of starch shifts the melting temperature (T_m) of the PBAT composite monofilament towards a lower temperature, and broadens the crystal melting peak. In terms of mechanical properties, the breaking strength of monofilament decreased to a certain extent, but the nodule strength retention rate increased from 63.86% to 97.56%, The infrared spectral absorption peaks of the two initial monofilament samples largely align with the characteristic peaks of pure PBAT and pure starch. Following the addition of starch, the monofilament's degradation performance significantly improved, with an average weight loss rate increase of 4.92%. The surface erosion of the monofilament intensified, and the holes and cracks deepened; Analyzing from an environmental perspective, the degradation rate of the monofilaments accelerates with rising temperature and increasing pH in the degradation environment. In this experiment, the seawater degradation performance of starch-based PBAT composite monofilaments was systematically studied, which can provide a reference for the development and application of new degradation materials for fisheries.