This paper introduces the REPA model, which stands for Regional Environmental Policy Assessment model. The REPA model is a multiregional computable general equilibrium model developed based on the GTAP-E model. The main objective of the REPA model is to assess potential impacts of implementing a set of environmental policy instruments (policy package) on economic, environmental and poverty indicators under regional economic integration in East Asia in terms of ASEAN Plus Three. This paper first sketches the basics of the GTAP model and GTAP-E model, the prototype of the REPA model, then explains the four modules, i.e. dynamic module, environmental module, policy cost module and poverty module, which are incorporated into the REPA model.