Abstract: This paper proposed a methodology on the assessment of groundwater environmental risk based on stochastic theory. A rectangular domain was taken as an example, random field of hydraulic conductivity coefficient is produced by Monte Carlo method, and spatially heterogeneous distribution of aquifer parameters is simulated. Subsequently groundwater flow and transport model are established and the pollutants migration in groundwater is calculated. The statistical frequency of pollution events in a large number of random simulations is considered to be convergent to pollution probability in sufficient simulation numbers, that is to say, pollution risk is reflected by pollution probability. The proposed method assumes that model parameters are random variable meeting a certain distribution characteristic, which avoids the arbitrary assessment with deterministic method. The conclusions obtained in this study can provide useful insights for site selection of factory and water source.