Quemoy has long been regarded as a border area in the cross-strait geopolitical strategy. Different forces with different political considerations have intervened in the affairs of Quemoy at different times, which resulted in the constantly changing identity of Quemoy. Based on field interviews and a thorough review of literature, and using the research methods of scale analysis and border studies, the authors examined the grassroots "border identity" in Quemoy. The redefinition process of the meaning of border was also discussed. This research concludes that, the "border identity" was gradually formed as a result of Quemoy residents' passive or active adjustment to changes in geopolitical relationship and borderlines between Taiwan and the mainland of China. In the temporal dimension, Quemoy has experienced several times of geopolitical changes during different historical periods, including the period of "Fan Qing Fu Ming" (rebelling against the Qing Dynasty and rebuilding the Ming Dynasty), Japanese-ruled period, the Nationalist Party-ruled period, and when the cross-strait "Three Links" were restored. In the spatial dimension, due to its special geographical position, and the fact that it used to be under the governance of different governments at different times, Quemoy has four different but interlacing scales of identity: it is a county, a province, and meanwhile an island and the community for the local residents. As a result, a local identity was gradually formed among the residents. They launched a series of social movements so as to get rid of the martial law imposed on Quemoy. From being passively adjusted to new situations, to actively utilizing the "border effect," the local people have re-institutionalized and reconstructed Quemoy's identity, changing it from a battle front into a peaceful trade island. This research provides a grassroots analytical perspective of geo-strategy and may help deepen the understanding for the cross-strait border area and China's reunification process. Apart from this, it will also contribute to the current studies on China’s border areas.