The invention relates to the soil improvement technology and the environment protection technology, in particular to a soil heavy metal passivant for the facilities vegetable field and a preparation method thereof for solving the problem that due to solid heavy metal pollution, the sustainable utilization of the facilities vegetable field is influenced. The soil heavy metal passivant for the facilities vegetable field comprises the following components in percentage by weight: 10 to 30 percent of medical stone powder, 10 to 30 percent of diatomite in powder, 10 to 20 percent of zeolite powder, 20 to 30 percent of lignite and 25 to 35 percent of fly ash. The preparation method for the soil heavy metal passivant comprises the following steps: mixing the medical stone powder passing through a 80-mesh screen, the diatomite in powder passing through a 80-mesh screen and the zeolite powder passing through a 80-mesh screen with lignite and uniformly stirring the mixture; and mixing the mixture with the fly ash passing through a 80-mesh screen, sufficiently stirring the mixture and after mixing uniformly, preparing the soil heavy metal passivant. The invention has simple preparation method and achieves the effects of passivating the soil heavy metals in the facilities vegetable filed and reducing the content of heavy metals in the soil which can be utilized by the crops by synergisticeffect of the components.