Abstract: To achieve the efficient resource utilization of coal gasification fine slag, a carbon-silicon composite was prepared via a high-temperature alkali activation-acid leaching process and applied for the adsorption of Methylene Blue. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman) and other characterization methods were used to analyze the morphological structure and physicochemical properties of coal gasification fine slag before and after high-temperature alkali activation-acid leaching treatment. The adsorption performance of the carbon-silicon composite for Methylene Blue was systematically evaluated. The results show that after alkali activation-acid leaching treatment, the graphitization degree of the carbon structure in the composite decreases, the content of amorphous carbon increases, and there are a large number of micropores and mesopores with a specific surface area of 668.49 m2/g. Under the conditions of a solid-liquid ratio of 0.1 g/L, an initial Methylene Blue concentration of 100 mg/L, an initial pH of 6.8, a temperature of 25 ℃, and a reaction time of 24 h, the removal efficiency of Methylene Blue by the composite can reach 80.6%, and the maximum adsorption capacity is 806.49 mg/g. The adsorption behavior conforms to the Langmuir isotherm model and pseudo-first-order kinetic model. After five cycles of regeneration, the adsorption capacity still remains at 61.6% of the initial adsorption capacity.