The purpose of this paper is to propose an evaluation method for coastal environmental restoration technologies using an ecosystem modeling technique. An ecosystem model of artificial lagoon, which is one of the environmental restoration technologies, has been developed based on field surveys at Rinku Park in Osaka Bay. Carbon and nutrient fixation effects of the artificial lagoon have been estimated as an index of the restoration efficiencies. The results of estimations have shown that the total fixation effects decreases year by year because of the accumulation of the sedimentary organic matter, and the fixation efficiency increases with decreasing the depth of the artificial lagoon.