Abstract: If there are potential dangerous sources of toxic chemical substances near the nuclear power plant, it will endanger the safety of the nuclear power plant. So the impact must be evaluated in the external human induced event assessment of the nuclear power plant. The preliminary screening can be carried out by the screening distance value for liquid toxic chemical substances around the nuclear power plants. In some cases, the dangerous sources should not be screened out, whereas the evaluation methods of the toxic chemical substances are not given in the correlative nuclear codes and guides. A kind of analysis and evaluation method was obtained by the research on the relevant domestic and foreign standards and literature, the leakage and evaporation quality in accident conditions can be calculated by a proper model firstly, and then the concentration of the location of the nuclear power plant can be calculated by a proper model for dispersion, lastly estimate the danger to the safety of the nuclear power plant by comparison with the concentration limits. The analysis and evaluation method will be expected to be beneficial reference in the impact assessment of the external human induced events of the potential dangerous sources of toxic chemical substances around the nuclear power plant.