The woody oil industry generates a large amount of seed shell waste during its production. Therefore, this paper employs a central composite design (CCD) methodology to optimize the ultrasonic-assisted extraction process, thus utilizing the byproduct. The infrared spectrum and thermogravimetric analysis is adopted to explore the chemical structure and thermal stability of tannin. Besides, the tannin resin (TF) is prepared to elaborate its adsorbing performance for dyes in water. The results verify the role of ultrasonic-assisted extraction method in increasing yield rate. The optimal conditions are as follows: 60% ethanol as extraction solvent, the solid-liquid ratio of 1:25 (g/mL), ultrasonic power of 160 W, and extracted at 80 o C for 60min. The yield rate of tannin under such conditions stands at 32.04% (w/w). Temperature is vital for the extraction rate. Acer truncatum tannin as a condensed tannin, performs favorable thermal stability, and TF effectively absorbs cationic dye in water. The maximum adsorption capacity of methylene blue peaks at 176.13 mg/g. Acer truncatum shell serves as a resource of condensed tannin, and Acer truncatum tannin resin can be potentially developed into a new biomass adsorbent.