This article challenges the justness of the concept “alien rule” in main Taiwanese democratization studies which have often been taken for granted rather than examined in depth. The article compiles various arguments to confirm the meaning of alien rule. The first contends that alien rule lacks legitimacy, and Taiwanese people regarded Nationalist government as alien rule after 228 Incident. The second proceeds from the regime’s origin and observes 3 aspects: 1. the spirit of state building and the highest goal of the state are extraneous, 2. the political regulation and structure are extraneous, and 3. The rulers controlling the state are extraneous instead of being consented by the ruled. Nonetheless, this article finds that most past quotation trying to prove the alien rule true stresses interviews and reports of certain local elites, which are questionable in sampling, logic and methodology. Besides, explanation utilizing faction and authoritarian oppression neglects that at the outset of Taiwan retrocession, factions were not established, interests were not accumulated, education and communication were not completed, and people were welcoming the regime. This article demonstrates that the first argument is constructed; the “settler state” interpretation in the second argument doesn’t give consideration to the fact that Mainlanders lead different lives, and the government didn’t protect them by proclamation; lastly, the article draws on Western voting behavior and identification theories, indicating that Taiwanese representatives were involved in the ROC’s constitution formulation, and Taiwanese people’s voting and Chinese identification tendency prove the legitimacy of the Nationalist government. Therefore, this article reasons that the government of the Republic of China migrating to Taiwan in 1949 is not an alien ruler. Instead, it is a political regime with legitimacy.