In this study, twelve cultivars of widely cropped rootstalk vegetables (4 cultivars each for radish, carrot and potato) and two typical soils (red soil and fluvo-aquic soil) were selected to study the sensitivity differences for mercury (Hg) through a greenhouse pot experiment. Two Hg addition treatments were applied, including low (equal to the national soil limit for Hg), and high (two folds of the soil limit for Hg) additions according to the second grade soil (the highest allowable soil heavy metal concentration for vegetable production; 0.3, 0.5, and 1.0 mg/kg for soils with pH<6.5, 6.57.5) of the Chinese Soil Environmental Quality Standard. The soil thresholds were then derived using species sensitivity distribution (SSD). The results indicated that biomass of edible part under Hg exposures varied with cultivars. Under high Hg addition treatment, Hg concentration in carrot cultivar Three red 8-inch grown in red soil, none in fluvo-aquic soil, exceeded the food safety standard (0.01 mg/kg). Cultivar consistently exhibited the largest effect on the Hg concentration in edible part compared with soil type. The SSD curves for Hg were fitted with Burr Ⅲ distribution based on the bioconcentration factor (ratio of Hg concentration in plant to that in soil) of the twelve cultivars. The 5% hazardous concentrations (HC5) were then derived inversely from the food safety standard. The Hg thresholds for red soil and fluvo-aquic soil were 0.53 and 1.2 mg/kg, respectively. This work provides an important reference for the revision of the soil environmental quality standard for heavy metals in China.