Chemistry core ideas play an important role in students' chemistry learning. On the basis of the representations of chemistry core ideas about "substances" and "processes" in the Chinese Chemistry Curriculum Standards (CCCS) and the U.S. Next Generation Science Standards (NGSS), we conduct a critical comparison of chemistry core ideas between these two documents in this paper. We also discuss the following reasons why there are differences in the representation of chemistry core ideas between them: different research perspectives on science education, different understandings of chemistry core ideas, and different understandings of the nature of teaching process. Our primary intent in this comparative analysis is to promote a deeper understanding of chemistry core ideas, provide advice and resources for chemistry curriculum research and chemistry teaching practice, and raise more attention on goals of science education and aims of chemistry.