In large geographic area, multiple sources release multiple stressors and affect multiple habits and endpoints. The diversity and complexity of the interaction between sources, stressors and habits is one of the challenges of Regional Environmental Risk Assessment(RERA) for large geographic areas. Meanwhile, the existed assessment methods do not pay enough attention on the release rules of risk factors, the distribution patterns of risk factors in space, and the path and the degree of the damage on receptors caused by risk factors. The theory of Risk Field(RF) was applied to analyze the generation mechanism of risk field and the influence mechanism on risk receptors. The environmental risk of Nanjing Chemical Industry Park was investigated as the example. At first, the environmental risk sources were identified. Then, methods, like Set Pair Analysis, were used to construct environmental risk field of various risk sources. After analyzing the environmental risk receptors in the risk field, the distribution of regional environmental risk level could be obtained. The densely populated areas or ecologically sensitive areas located around the risk sources or the river downstream had higher environmental risk level(environmental risk value R≥6), which was in good agreement with the actual situation. This paper suggested establishing the prevention-oriented environmental risk management system based on the classification results of the environmental risks.