Interstate electric power system, as an alternative for energy cooperation under regional economic block, has been hotly debated before progressing the restructure in electric power industry and rapidly expanded in many regions after 1990s. Especially, since northeast asia has strong supplementation in resource, load shape, fuel mix etc., interconnection of electric power systems in this region may bring considerable economic benefits. This paper implements a mathematical optimization model, ORIRES, proposed by Russia, in analysing the economic feasibility of system interconnection. Additional analyses on the environmental impact of the system interconnection, and sensitivity of key factor inputs have been performed.