Abstract: Lignin-based carbon quantum dots(CQDs) were prepared with calcium lignosulfonate as precursor by molecular self-assembly and ultrasound-assisted method at room temperature. The effects of calcium lignosulfonate and NaBH₄ on the fluorescence property of CQDs were studied, and the synthesis condition of CQDs was also optimized. The optimal preparation conditions were as follows: the mass concentration of calcium lignosulfonate was 60 g/L, the mass concentration of reducing agent NaBH₄ was 50 g/L. The structural morphology and optical properties of CQDs were confirmed by transmission electron microscopy(TEM), infrared spectroscopy(FT-IR), X-ray photoelectron spectroscopy(XPS), UV-visible spectroscopy(UV-vis), and fluorescence spectroscopy(FL). The experimental results showed that CQDs had small particle size((9.5±0.5)nm), uniform distribution, no agglomeration phenomenon, excellent optical properties, and fluorescence quantum yield of 12.4%. In addition, CQDs were used to investigate the effect of different silver ion concentrations on the fluorescence intensity. The results showed that CQDs had good fluorescence recognition and sensitivity to Ag⁺, with a linear detection range(R²=0.998) of 0-250 μmol/L and a detection limit of 525 nmol/L. Meanwhile, CQDs fluorescence showed excellent selectivity and low cytotoxicity, which was expected to show potential application value in biosensing and environmental detection fields.