Professor Petersmann has developed a constitutionalization theory for IEL based on Western constitutionalism theory in conjunction with human rights law. However, there is a paradox in his theory considering that he stresses ‘legal pluralism’ on the one hand, while calling for a cosmopolitan conception of IEL on the other hand. The hypothesis of this paper is that there are no ‘universalizable’ principles and common constitutional principles that can guarantee the compatibility between the two. Petersmann’s three often-used keywords, ‘human rights,’ “principles of justice,” and “judicial protection of individual rights,” are clarified in the context of Chinese thought and China’s progressive integration into the world economy. This paper finds that Petersmann’s theory focuses on bottom-up individual struggles, whereas Chinese thought is characterized by top-down overall consideration. The value divergence between the goodness of human nature in Chinese thought and the evil of human nature in Western thought makes ‘legal pluralism’ an insurmountable obstacle to a cosmopolitan conception of IEL.