In this study, we try to present the framework of an integrated evaluation model, which drives an optimal allocation of environmental investment in order to conserve water environment of the Sea of Japan, and we also analyze an impact for the seawater quality due to land-based water pollutant from socio-economic activities of coastal area. The target regions are coastal area of the Sea of Japan, which includes some parts of Japan, South Korea, China, and Russia in Northeast Asia. To propose a feasible solution of decision making for integrated ocean management, a dynamic system simulation model is formulated as a linear programming problem maximizing an objective function with defined sub-models taking into account of environmental investment policy. The sub-models consist of the structure of water pollutant inflow, air pollutant emission, and socio-economic activities in the target area to simulate environmental and socio-economic dynamics. Furthermore, we quantitatively make an analysis of the influence on seawater quality by land-based water pollutant flowing into the Sea of Japan. JEL classification: C61, P49, Q53, Q56, R19