By hydroponics experiment, the effects of main base anions（NO3-、SO42-、SiO32-） on Cr(VI） toxicity of pakchoi cabbage (Brassica campestris L．ssp．chinensis(L.)) and its mechanism were studied. The results showed that: ①With the increase of Cr content in water culture, the growth of pakchoi cabbage and its iron uptake were restrained obviously by Cr, therefore the activity of nitrate reductase and the metabolism of carbon, nitrogen were also inhibited intensively, which showed that Cr was highly toxic to pakchoi cabbage in this hydroponics experiments. ②Cr uptake by pakchoi cabbage can be promoted significantly by nitrate anions (NO3-), and from it the inhibition of iron uptake by pakchoi cabbage reduced and leaf nitrate reductase activity which abated by Cr in nutrient solution was also mitigated, showing that the toxicity of Cr to pakchoi cabbage can be mitigated by nitrate anions when applied properly. ③On the condition of the same content of Cr in nutrient solution, at the proper range, with the increasing of sulfate anions (SO42-) concentration in nutrient solution, Cr uptake by pakchoi cabbage decreased obviously and leaf nitrate reductase activity was also enhanced. However, high sulfate anions concentration in water culture resulted in salt toxicity somewhat to pakchoi cabbage and therefore reduced its resistance of Cr toxicity. ④It obviously showed that Cr uptake by pakchoi cabbage can be restrained from the increase of silicate anions concentration in water culture, but there was no positive effect in leaf nitrate reductase activity from these effects of silicate anions, and the growth of pakchoi cabbage which restrained by Cr was also not obviously promoted by it, showing that these effects on Cr uptake by silicate anions can not obviously detoxify for pakchoi cabbage. In this study, results showed that the proper rate of nitrate concentration is the key that restraining Cr uptake by pakchoi cabbage in water culture, and it was an effective technological measure to restrain Cr uptake by regulating the ratio of base anions according to this hydroponics experiment.