Teacher emotions are essential for teaching effectiveness and teachers' professional development. Studying teacher emotions during a program in today's world is crucial, where teachers are commonly involved in professional development programs. From an ecological perspective, this study employed a case study method to examine the emotions of two Chinese high school mathematics teachers in a 4-year teaching improvement program. Semi-structured interviews, teacher emotion logs, researcher memos, and informal dialogues were all used to collect data. This study aimed to better understand the emotions that Chinese high school mathematics teachers developed and the processes that generated them in their interactions with various ecosystems within a specific professional development program overlay. The study's findings revealed that the two teachers triggered 65 emotions in their interactions with the various ecosystems over 4 years-A describing 51 and B describing 46-with an overall predominance of positive emotions. They triggered the broadest range of emotions in the mesosystem, particularly during interactions with program companions. During the early, medium, and late stages, their internal psychological factors and interactions with each system changed, resulting in significant changes in their emotions. They all went through phases of mixed sadness and happiness, ending in a state of delight and calmness. Finally, we recommended teachers' professional development based on the study's findings.
