Abstract: Biomass, as an abundant renewable and carbon-neutral energy source, holds significant potential in the field of thermochemical hydrogen production. However, conventional steam gasification processes commonly suffer from low hydrogen yield, substantial CO₂ emissions, and challenges in controlling nitrogen and sulfur pollutants. The sorption-enhanced steam gasification of biomass using Calcium-based materials can improve hydrogen concentration and yield, with in-situ CO₂ capture by Calcium-based materials. To enhance biomass gasification for hydrogen production and elucidate nitrogen-sulfur transformation characteristics during this process, t high-sulfur marine biomass （Sargassum） was utilized as feedstock. Based on the Aspen us simulation platform, a thermodynamic model coupling CaO carbonation-calcination cycles was developed to investigate the role of CaO absorbent in CO₂ capture during gasification and its regulation of steam reforming reaction equilibrium. Systematic analysis was conducted on the effects of reaction temperature, mass ratio of steam to biomass （m（S）∶m（B））, and calcium-to-carbon molar ratio （n（Ca）∶n（C）） on gas product composition, carbon conversion rate, syngas calorific value, and nitrogen-sulfur conversion characteristics. Results indicate that through parameter optimization, optimal conditions of gasification temperature （800-850 ℃）, mass ratio of steam to biomass （m（S）∶m（B）） （0.6−0.8）, and calcium-to-carbon molar ratio （n（Ca）∶n（C）） （1.5−2.0）, a molar ratio of H₂/CO exceeding 3.5 can be achieved, achieve a carbon conversion rate exceeding 94% and a low-heat-value syngas of 11.8−12.1 MJ/m³. with a low calorific value of 11.8−12.1 MJ/m³. Simultaneously, calcium-based materials effectively regulate nitrogen and sulfur migration pathways through dual mechanisms of chemical adsorption and catalytic conversion, keeping total NH₃ and HCN below 35×10⁻⁵, achieving N₂ selectivity exceeding 85%, and H₂S removal rates surpassing 96%. Sulfur is primarily solidified as CaS, significantly reducing pollutant emissions. This research provides a theoretical foundation and process optimization pathway for the industrial application of hydrogen production via gasification of high-nitrogen, high-sulfur marine biomass, advancing the development of low-carbon hydrogen production and efficient carbon capture technologies.