Arsenic is one of the most toxic heavy metals in water and soil pollution. Biochar, as a high-quality remediation material, has been widely used as an adsorbent for remediation of arsenic-polluted water and soil. However, the adsorption capacity of biochar has certain limitations, so modifications have been made to enhance its adsorption ability for arsenic. Selenium is an essential trace element for plants, promoting plant growth and also competing with arsenic, making it an excellent modification material. We studied the selenium-modified rich biochar and original selenium-rich biochar, including their production, physicochemical properties, and arsenic adsorption mechanism. Selenium-rich biochar and selenium-modified biochar showed no significant differences in properties, arsenic adsorption efficiency, promotion of plant growth, and selenium enrichment effects, both being excellent materials for arsenic remediation. The theoretical maximum adsorption capacities (qm) for As(III) on raw biochar, selenium-modified biochar, and selenium-enriched biochar were 49.87 mg/g, 55.89 mg/g, and 59.00 mg/g, respectively, with the selenium-enriched biochar exhibiting the highest adsorption capacity. The results of planting experiments indicate that, compared to the original biochar, both selenium-enriched biochar and selenium-modified biochar significantly enhanced growth promotion and adsorption efficiency by 24.68 %, 24.35 %, 59.50 %, and 64.64 % respectively. However, the preparation cost of selenium-modified biochar is high, making it challenging to promote, with a total cost price 84.31 % and 83.40 % higher than selenium-rich biochar. It is evident that selenium-rich biochar not only possesses the efficacy of selenium-modified biochar but also has the advantage of low cost, making it a material with significant potential for arsenic remediation.