Abstract: Remediation efficiency is one of the main factors affecting the remediation cycle and promotion of remediation technology. Pot experiments were carried out with paddy soil with different pH and different Cd concentration. The w(Cd) of heavily contaminated soil (SKS) was much higher than the risk intervention value in Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018). The w(Cd) of moderately contaminated soil (pH were adjusted and stabilized to about 3.97, 4.97, 6.03, 6.90 and 7.93, respectively) was between the risk screening value and intervention value, and the w(Cd) of lightly contaminated soil (YH) was slightly higher than the risk screening value. The soil Cd availability, speciation distribution and w(Cd) before and after treatments at different pH and different Cd concentration were compared, and the main factors affecting the remediation efficiency were further studied by PCA and Pearson correlation analysis. The results showed that:(1) Compared with the original soil, the decrement of the w(available Cd), w(acid soluble Cd), w(reducible Cd), w(oxidizable Cd) and the w(Cd) of the treated soil with different pH increased with decrease of pH. When pH ≤ 6.0, the remediation efficiency was significantly improved compared with the treatments of pH>6.0 (P < 0.05). (2) After remediation, the w(Cd) of YH decreased to below the risk screening value. The w(Cd) with soil pH ≤ 6.0 of moderately contaminated soil was reduced to 0.60 mg/kg, while the w(Cd) with soil pH>6.0 was still higher than 1.00 mg/kg. (3) The soil of SKS treatment had the highest w(available Cd), and there was no significant difference in biomass between SKS and YH, the w(Cd) of Sedum plumbizincicola could reach 681.5 mg/kg, but the remediation efficiency was significantly lower than other treatments (P <0.05). Taking into account the results of the PCA and Pearson correlation analysis, in addition to soil pH, Cd availability and the biomass, the bio-concentration factor (BCF) of S. plumbizincicola also played an important role in the efficiency of remediation. Therefore, phytoremediation with S. plumbizincicola is more suitable for the moderately and lightly Cd-contaminated and acid soils, while for phytoremediation of alkaline or heavily contaminated soils, the remediation cycle can be extended or the efficiency could be improved by combining other remediation techniques.