Abstract: Effective prevention and control of invasive alien species remains a technical challenge, and their resource utilization offers a new approach for managing invasive plants. This study used stems and a mixture of stems and leaves of the invasive plant Erigeron canadensis L. to prepare biochar under limited oxygen conditions at 300℃, 500℃, and 700℃, followed by modification with sodium hydroxide（alkali） and citric acid（acid）. The differences in physicochemical properties—including yield, pH, specific surface area, functional groups, mineral composition, and morphology—of biochar produced from different plant parts, pyrolysis temperatures, and modification methods were systematically compared. The adsorption performance for As（Ⅲ） and Cd（Ⅱ） in aqueous solution was also investigated.The results showed that as the pyrolysis temperature increased from 300℃ to 700℃, the biochar yield decreased from 51.26% to 19.69%, while the pH increased from 9.79 to 12.28. The specific surface area increased significantly, and acid/alkali modification further enhanced it. Specifically, acid-modified ECBC prepared at 700℃ exhibited the largest specific surface area of 108.13 m²/g, which was 178% higher than that of the unmodified biochar. FTIR analysis revealed that the abundance of some oxygen-containing functional groups such as hydroxyl（-OH） and carboxyl（-COOH） decreased with increasing temperature but increased after modification. XRD analysis confirmed the presence of abundant minerals in the biochar, with ECBC showing a greater diversity of mineral types.In a 20 mg·L⁻¹ heavy metal solution, ECBC700 achieved a removal rate of 99.1% for Cd（Ⅱ）, significantly higher than that for As（Ⅲ） （14.4%）. The biochar exhibited high adsorption performance for As（Ⅲ） in lower pH solutions and for Cd（Ⅱ） in higher pH solutions. The pseudo-second-order kinetic model （R² > 0.99） indicated that the adsorption of As（Ⅲ） and Cd（Ⅱ） onto Erigeron canadensis biochar was dominated by chemical adsorption. The unmodified biochar ECBC700 showed the highest adsorption potential for Cd（Ⅱ）, while the acid-modified ECBC700 exhibited the highest adsorption potential for As（Ⅲ）. This study revealed the multi-mechanism synergistic adsorption of As（Ⅲ）and Cd（Ⅱ） by Erigeron canadensis biochar, demonstrating its potential for the resource utilization of invasive plants and heavy metal remediation.