In practical operations, crosswinds significantly impact the thermal performance of mechanical draft cooling towers (MDCTs). This paper investigated the beneficial impact of deflector plates to mitigate the adverse crosswind effects on the thermal performance of MDCTs. The mechanism by which deflector plates reduce the crosswind effects was elucidated from both the windward and leeward sides. Additionally, the performance optimization with varying crosswind angles and speeds was comprehensively analyzed. Results revealed that at lower crosswind speeds, deflector plates effectively streamline airflow on both windward and leeward sides. However, when wind speeds exceed 4 m/s, the vortex region on the windward side expands, reducing the effectiveness of airflow optimization by deflector plates. Nonetheless, deflector plates consistently mitigate crosswind effects on the leeward side. Within the investigated parameters, at a 0° crosswind angle and 1 m/s crosswind speed, deflector plates significantly enhance thermal performance, manifesting in a 0.362°C reduction in outlet water temperature, a 10.77% increase in Merkel number, and a 2.48% improvement in cooling efficiency. This research establishes a theoretical framework for optimizing thermal performance in MDCTs with crosswind effects and provides valuable insights for engineering applications.