The invention discloses a heavy metal passivating agent suitable for acidic cadmium polluted soil in paddy fields in south China. The heavy metal passivating agent is prepared from nonmetal silicate minerals, fly ash, calcium hydroxide and phosphate. The nonmetal silicate minerals have a good absorption effect on heavy metal ions; calcium hydroxide and phosphate can increase the pH of the soil, and improve the acidity and alkalinity of the soil. The heavy metal passivating agent has the following advantages that the passivating agent has good and stable repair effects on acidic cadmium or neutral cadmium moderately-polluted or slightly-polluted farmland soil, the required cost is low, the use amount is little, the normal growth of rice in the cadmium moderately-polluted or slightly-polluted paddy-field soil can be achieved by applying a small amount of the passivating agent, the applied passivating agent has no negative effect on the soil, and secondary pollution is not caused.