The fishing activities and administrative management are important historic grounds for Chinese sovereignty over the Nansha Islands according to 'effective occupation' in the international law.Effective occupation is the key step for a nation to acquire territorial sovereignty based on the occupation principle in the international law. In the remote or harsh areas, the requirements of effective occupation could be reduced appropriately, if only the occupying state exercises and demonstrates the sovereignty which is appropriate to the territory situation. The Nansha Islands of China is far away from the mainland, and the natural conditions are adverse. Since the ancient times, fishery is one of the most important ways for the development and management of the Nansha Islands. The fishery history of the Nansha Islands in China not only proves that China discovered the Nansha Islands firstly for the navigation and fishery development, but also confirms that China has implemented jurisdiction over them on account of the administrative management over fishery activities which is corresponding to the Nansha Islands and its adjacent waters, and occupied the Nansha Islands effectively, and therefore has owned the sovereignty over them.