This paper proposes an innovative semi-Markov jump power system $H_{\mathrm{\infty }}$ load frequency control (LFC) strategy, incorporating an adaptive event-triggered mechanism (AETM) to enhance control efficiency and stability under complex environmental conditions. Specifically, to address power system uncertainties caused by environmental factors, we first modeled the system using a semi-Markov jump process, effectively capturing its dynamic variations across different operational states. Subsequently, to reduce communication and computational burdens, we introduced a novel AETM that selectively determines triggering conditions, thereby avoiding unnecessary control signal updates. Furthermore, we constructed multimodal asymmetric Lyapunov-Krasovskii functionals (LKFs). By relaxing constraints on matrix symmetry and positive definiteness, this method reduces the conservatism of stability criteria, ensuring stable system operation and maintaining strong robustness even in the presence of external disturbances. Finally, simulation results validated the effectiveness of the proposed strategy, demonstrating its capability to significantly enhance power system control performance and stability while effectively reducing resource consumption.