Pedagogical content knowledge plays an indispensable role in teaching practice and has become an important category of research and practice for scholars and teachers. This article endeavors to delve into the influence of mathematics teachers' pedagogical content knowledge on the classroom learning atmosphere. Through the perspective of classroom recordings, it deeply analyzes the infectious effect of pedagogical content knowledge on students' learning experience and emotional engagement. This article employs qualitative analysis methods, utilizing encoded data, to dissect the application of teachers' pedagogical content knowledge, the status and feedback of students in mathematics classrooms, in order to unearth the relationship between the two. Research has found that the appropriate application of pedagogical content knowledge by mathematics teachers can have a positive impact on the learning atmosphere of students in the classroom. The artful use of humor by teachers has the power to visualize dull mathematical knowledge. It not only sparks students' interest and enthusiasm for learning but also contributes to the cultivation of high-quality classroom instruction. This precisely reflects the crucial role of teaching strategy knowledge in pedagogical content knowledge. The study reveals the mechanism by which mathematics teachers' pedagogical content knowledge plays a role in creating a positive learning atmosphere, providing beneficial insights for teaching practice.