Abstract: Public health and public security events present the importance of crowd dynamics observation. The crowd dynamics observation should be a key component of human-orient observation, and the necessary elements of global observation system framework consisting observations of space, sky, land, ocean and people. This paper firstly introduces a concept of crowd dynamics observation, defines its scientific connotations and boundaries, and highlights the role and significance of this theory. Then, from the perspective of public health and safety emergency, this paper analyzes the characteristics of accuracy, scientific city and on-demand in crow dynamics observation requirements, and introduces the state of art of crowd dynamics observation including data perception of crowd dynamics, sampling and expansion of population scale, and quantitative modeling of crowd dynamics, crowd dynamics research field, etc. Next, this paper thinks about the observation tasks of crowd dynamics from four important aspects, such as, rigorous distinction between individuals and groups, abnormal observations centered on spatiotemporal processes, breakthroughs in observational thinking under missing data, and scientific predictions of crowd dynamics under specific scenarios, etc. Finally, this paper summarizes three important research challenges combined with public health and safety emergency tasks, namely, the challenge of improving observation capabilities, the challenge of fusion observation of human and earth observation, and the research ethical challenge of human observation. In short, the concepts, thinking dimensions and challenges proposed in this paper provide basic theories and methods for major public health and safety emergencies, clarifying the laws of urban multi-type spatial development, mastering the differentiation mechanism of spatial evolution, and controlling urban spatial development paths. All of them show assignificance of the frontier exploration.