With the economic development and deregulation of China, the cross-strait social interaction and economic cooperation are becoming so frequent that contributes to the growing national security problems of Taiwan. So far, the Mainland China has been the major threat to Taiwan. And the scopes of cross-strait national security consist of not only the traditional military threat but the nontraditional security issues as well. Among them, the phenomenon of the illegal Chinese immigrants causes great havoc as well as threat to the immigration management and social order of Taiwan. This study is to tackle the following three problems. First of all, to define the impacts of the illegal Chinese immigrants to Taiwan through the concept of nontraditional security. Second, to analyze the impacts of the illegal Chinese immigrants to the international society through the concept of legal and illegal immigrants. Finally, to elaborate the status quo of the illegal Chinese immigrants and disclose the outcomes and seriousness of them by the means of cases study. As far as Taiwan is concerned, the phenomenon of the illegal Chinese immigrants sways its nontraditional security issues in terms of political, social, and economic area. Since the party rotation in 2008, the Taiwanese government has taken more open and active attitudes toward cross-strait interaction and the cross-strait relations have obviously improved. In addition, Taiwan has lifted the ban on the Mainland China policy, such as permitting Chinese tourists to enter Taiwan, direct charter fight, Three Direct Links, and the individual travel program for Chinese tourists. There are more and more diverse channels for mainlanders to enter Taiwan. Facing these illegal activities and the consequent impacts on the national security and social order of Taiwan, the Taiwanese authority concerned should reinforce related measures to eliminate its threats resulting from the nontraditional security in order to strengthen the self-defense capacity.