With the effective control of exogenous pollution in lakes and reservoirs, sediment pollution characteristics have become a key factor affecting the water environment quality of these freshwater systems. Sulfate-rich Tanghe Reservoir is chosen as the investigated reservoir. We explored the spatial distribution characteristics of physical and chemical properties, contents of total amount of heavy metals, acid volatile sulfide (AVS), and simultaneously extracted heavy metals (SEM) of sediments of the reservoir. Meanwhile, ecological risks and toxic effects induced by heavy metals were evaluated using sediment quality guidelines (SQGs) and method of AVS-SEM relationships. The results showed that the AVS content in the sediment of Tanghe Reservoir ranged from 0.03 to 51.75 μmol/g, and displayed a decreasing trend in the order of the deepwater area before the dam> east tributary reservoir> west tributary reservoir. According to the Pearson correlation analysis results, spatial distribution difference of AVS in the sediment of Tanghe Reservoir showed a significant positive correlation to the SO₄^2- concentration and LOI content in the porewater and sediment, and showed a significant negative correlation to the NO₃^- concentration and pH value in the porewater. The ΣSEM content in the sediment of Tanghe Reservoir ranged from 0.03 to 51.75 μmol/g, and display a decreasing trend in the order of the east tributary reservoir > deepwater area before the dam> west tributary reservoir. Ranges of ΣSEM/AVS and ΣSEM-AVS in the sediment of the reservoir are 0.06-22.73 and -49.18-2.44 μmol/g, respectively, which showed that the surface 0-10 cm sediments in the deepwater area before the dam were not ecologically risky, and the SEM in the sediments of the East and West tributaries could not be completely fixed by AVS and showed potential ecological risks. In terms of single heavy metals, Ni, Cu, Pb and Zn might have potential biotoxic effects in the deepwater area of dam and middle area of west and east tributary in the reservoir. However, the toxic of Ni was close to intermediate and should be given special attention in the future. High content of AVS is prone to occur in the sediment of sulfate-rich reservoirs, concentrations of SO₄^2- and NO^-₃ in porewater are the vital factor determining the net yield of sediment AVS. The background values of heavy metal soils in the watershed and the types of wastewater discharged by industrial and mining industries directly affect the types of heavy metals that induce ecological risks.