Abstract: The research on theories is essential to advance the People's Congress system with the times. In order to deepen the theoretical research on the People's Congress system and clarify the basic concepts, categories, and principles of the People's Congress system, this article discusses some important basic theoretical issues, including the concepts of the People's Congress system in broad and narrow senses, the People's Congress system as the fundamental political system of China, 'unity of legislature and administration' for the People's Congress system, the People's Congress as a supervisor and supervisee, and the relationship between the People's Congress and the ruling party.