A new drilling fluid additive-biomimetic strengthen wellbore stabilizer(JBWDJ) was prepared to solve the issue of wellbore collapse and instability in weakly cemented argillaceous unconsolidated sandstone natural gas hydrate reservoirs in the South China Sea. JBWDJ was developed by imitating the adhesion mechanism of mussel catechol groups underwater environment in this study. Polyvinyl alcohol(PVA) with the property of film-forming and tannic acid(TA) rich in catechol and pyrogallol groups were used based on hydrogen bond. It enhanced hydrate reservoir stability from three aspects: actively improving the bonding strength between clay mineral particles, inhibiting clay hydration dispersion and expansion, and stabilizing hydrate configuration. The experiment results showed that the core soil blocks soaked in JBWDJ for 16 hours remain complete in shape and have a certain compressive strength, while treated with solutions including water, polyacrylamide, and polyamine inhibitors are all in a loose sand shape. The compressive strength of the artificial core treated by 3%JBWDJ increased by 2.01 times compared with untreated core samples. Additionally, the adhesion force between atomic force microscope(AFM) probe modified by SiO2 microsphere and 5% JBWDJ reached 2314 nN. Shale cuttings treated with 3% JBWDJ had a rolling recovery rate of 80.85%, which can significantly improve the recovery rate of rock cuttings compared with rock cuttings treated by clean water(48.4%), polymer wellbore stabilizer(52.35%), and potassium chloride(26.3%). The core expansion height of the drilling fluid containing 3% JBWDJ is only 0.9 mm, compared with the core soil block expansion height treated by the drilling fluid system without JBWDJ, the expansion height can be reduced by 50%. Rheological testing and reservoir protection experimental evaluation show that the JBWDJ has good rheological properties and certain reservoir protection capabilities. Microscopic analyses including transmission electron microscopy(TEM), infrared spectroscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy(EDS) revealed the mechanism of JBWDJ. It is mainly to build a network structure through hydrogen bonding, adsorb on the surface of the rock, enhance the bonding between clay mineral particles, and form a dense biomimetic film on the surface. Meanwhile, it has a good effect on inhibiting the hydration expansion and dispersion of clay, thereby achieving the goal of improving the compressive strength of rock cores and strengthening reservoir stability. Furthermore, in-situ Raman spectroscopy comparative analysis showed that JBWDJ has no impact on the structure of type I methane hydrates. Hopefully, through the above mechanical performance testing and microscopic mechanism characterization, it can provide new materials for ensuring the stability of hydrate reservoir wellbore.