Soil heavy metal pollution presents a significant environmental challenge globally, with cadmium (Cd) pollution being highly severe and posing risks to both soil ecological security and human health. Biochar offers advantages such as reduced costs, stable chemical properties, a micro-porous structure, and an expansive, specific surface area that aids in the fixation of heavy metals in soil. However, there has been little research on the adsorption mechanism of sulfur-modified biochar. Indigenous woody peat (BC) was used as a biochar substrate to evaluate the immobilization effectiveness of sulfur-modified woody peat (SBC) in Cd-contaminated soil in terms of cadmium and to determine the adsorption mechanism. Electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that the S element was loaded on the surface of woody peat materials. X-ray photoelectron spectroscopy (XPS) analysis indicated that Cd in woody peat biochar is adsorbed mainly through the formation of Cd(OH)2 and CdCO3 precipitates. Additionally, SBC facilitated the interaction between Cd and organic sulfur, leading to the formation of more stable CdS and CdHS+ that were not easily dissolved or oxidized. The study also examined the adsorption mechanism. The results indicated that the material adhered to the second-order kinetic adsorption model. SBC had a greater capacity than BC to adsorb Cd, approximately six times greater. The soil culture experiment yielded varying effects with the addition of SBC and BC, notably on the soil pH and available Cd content. Adding 1% SBC resulted in a 12.5% increase in soil pH to a level of 7.52. After a 1% SBC treatment, the availability of Cd in the soil reduced significantly, with only 4.01 mg/kg found, which was significantly different from the control (CK) treatment (P < 0.05). These results suggest that SBC has promising potential for pollutant remediation applications.