Abstract: The controlling of water quality is a key factor for aquatic production. In recent years, chemical and physical water-treatment methods have been used in aquatic species and aquaculture production, which has a certain effect in improving the growing environment of the aquaculture. But there are still kinds of shortages existed. In this paper, seawater sterilization was studied by the little electrolysis technique of the nanocatalyst, which expected to ascertain the minimum value of completely sterilization. And tolerance range of free chlorine in the aquaculture water was studied by different levels of treatment intensity of this technology. The result showed that when the treatment intensity was 1.06 W·h/t, the sterilizing rate could be 100%. And the cost was 0.00053 yuan per ton seawater. The highest tolerance intensity for the grouper fry was 4.08 W·h/t. And under this intensity, it could reach the best effect of sterilization and continuous bacteriostatic. And this intensity could be used in practical production of offspring seed. Using the little electrolysis technique of the nanocatalyst to produce the free chlorine, we could disinfect pathogenic organisms, and further purify water, and expect to suppress the occurrence of pathogenic diseases in the end. Finally, the promotion of the little electrolysis technique of the nanocatalyst could have a certain value and environmental effect in aquaculture.