This study examines why household registration systems inherited from socialist planned economies followed divergent trajectories in China and Vietnam after market-oriented reforms. In China, the hukou (戶口) system became increasingly linked to education, housing, social insurance, and land-based urban finance in first-tier cities, functioning as a sorting mechanism that stratifies urban citizenship. In Vietnam, by contrast, the hộ khẩu system was gradually relaxed after Đổi Mới, and the 2020 Law on Residence abolished the paper household registration book while prohibiting discrimination based on residence status. The study explains this divergence by focusing on how the two communist parties organized society during the revolutionary and land reform periods. The Chinese Communist Party directly reorganized rural society into administrative categories, thereby institutionalizing its authority to classify the population. The Vietnamese Communist Party, in contrast, built state authority through prolonged war and national division while relying on village communities and local discretion. This historical formation made it possible for Vietnamese society to challenge the legitimacy of population classification through household registration and to demand institutional correction. Through a comparative-historical analysis, this study traces the formation of the two systems and examines Shanghai and Ho Chi Minh City to show how national-level divergence is translated into distinct forms of urban citizenship.