The invention provides a composite passivator applicable to rice field soil cadmium pollution. The composite passivator is mainly prepared from chitosan, sodium bentonite, bone meal, lime, charcoal, ZnO and nanometer FeO. The invention further provides a preparation method and application of the composite passivator. By means of the composite passivator, the available cadmium content in rice and the cadmium content in rice can be remarkably reduced, the soil pH value can be improved, vast rice soil polluted by heavy metal cadmium can be treated, the organic matter content is greatly improved, and the soil biology-chemical characteristic is improved.