Abstract：Through the considerable improvement of risk assessment system, uncertainty remained a primary threat to the confidence level of risk assessment. Under the primary definitions of uncertainty in environmental risk assessment home and abroad, owing to the realistic and theoretical limit, choosing the relatively suitable model was considered to be much more important step to the risk assessment process concerning the reduction of uncertainty. In particular, model uncertainty probably made a much bigger effect than that of parameter uncertainty. This study quantified the effects of different sources of uncertainty and developed a screening procedure to choose the relatively suitable model on basis that 3MRA, MMSOILS and CalTOX models combined with Monte Carlo simulation were applied to the same contaminated site and the typical receptor. The 6-steps comprehensive assessment procedure would be an important reference to future health risk assessment of contaminated sites.
