Abstract: Macroalgae play a very important role in marine ecosystem restoration by absorbing large amount of nitrogen and phosphorus, and fixing CO₂ from the air through the photosynthesis process. Saccharina japonica is one of the essential macroalgae species in China, which has both economic and ecological value. In this paper, VENSIM was used to build the mathematical model for S. japonicagrowth. Results show that the model can simulate well the growth process of S. japonica under different environment conditions. The sensitivity was calculated by Morris function through which the importance of different environmental parameters can be analyzed. Results find that temperature and light were the two key factors which impact the growth of S. japonica mostly. The light influence was greater at the early period of cultivation while the temperature limited more at the harvesting stage. In general, the nutrients cannot limit the growth of S. japonica except on the areas of large culturing scale and high density (culturing). The impact of nitrogen was greater than phosphorus when nutrient limitation happened. The model built in this paper can provide a better way to simulate and analyze how the environmental parameters will impact the growth of S. japonica under different sea conditions, thus it can help on the macroalgae culture management.