A pot experiment was carried out to study effect of application of Ni on growth and uptake and accumulation of mineral nutrients of pakchoi in brown soil, and critical value for soil Ni pollution to be toxic to pakchoi through monitoring change in biomass production of pakchoi. The critical value is characterized by Ni content in the shoot and content of available Ni in the soil. Results showed that biomass increased significantly with the increase in Ni application rate within the range of 0~25 mg/kg, while it decreased obviously when the Ni application rate beyonded 25 mg/kg. The uptake of mineral nutrients of the plant showed a certain relationship of synergism or antagonism to Ni content. With the point where biomass droped by 10% set as the critical point for soil Ni pollution to be toxic to pakchoi in brown soil, the critical value is 66.36 mg/kg for total Ni, 6.21mg/kg for available Ni (DTPA), and 16.40 mg/kg for Ni content in stem and leaves.