Teaching in a Hyflex environment poses unique emotional challenges for EFL teachers, who must navigate the complexities of both in-person and online instruction. Managing these demands often requires significant emotion labor, where teachers regulate their emotions to meet professional expectations. Despite the critical impact of these emotional demands, longitudinal investigations concerning the dynamics of EFL teacher emotion labor and its association with emotional vulnerability remain limited. To address this gap, we conducted a 16-week study tracking the emotion labor strategies of four Chinese university EFL teachers across 32 hyflex classes—a dual-mode approach that combines face-to-face and online instruction. Employing time series analyses, we identified dynamics in the teachers’ emotion labor over time. Subsequent focus-group discussion was conducted to gain insight into the factors influencing these changes that resulted in teachers’ emotional vulnerability. These factors encompassed the necessity for more suitable technology in the context of hyflex teaching, the impact of large-scale mid-term tests, and the intricate interplay between emotion labor strategies and teachers’ inner fears. Our findings highlight the crucial role of universities in supporting EFL teachers in adapting to the demands of online teaching, managing external pressures, and navigating the inherent tensions of emotion labor, which alleviates teachers’ emotional vulnerability. By understanding and addressing teachers’ emotional needs, we can foster positive teaching experiences and promote a conducive learning environment in the evolving landscape of online hyflex teaching.