Pyropia yezoensis, a typical intertidal macroalga, is frequently exposed to various abiotic stresses in its natural habitat. This study characterized the morphological, physiological, and transcriptomic responses of P. yezoensis thalli under high-light stress to explore its adaptive mechanisms. High irradiance slightly promoted thallus elongation and cell division but significantly decreased blade thickness, ultimately reducing overall biomass accumulation. Thylakoid lamellae became thinner and more loosely arranged. Photosynthetic physiology, pigment composition, and metabolite contents decreased, while reactive oxygen species were induced. By isolating high-light stress from heat stress, we conducted genome-wide transcriptomic analysis to delineate photo-stress responses, revealing that P. yezoensis prioritizes energy allocation towards emergency responses by reducing high-energy-consuming biological processes and metabolic activity, thereby enhancing survival under environmental stress. Notably, NADPH-dehydrogenase-dependent cyclic electron transport (CET) played a more critical role in overall CET contribution under high-light stress. Furthermore, the mitochondrial alternative oxidase (AOX) pathway, responsible for dissipating excess reducing equivalents, was not significantly activated, which may be a reason why P. yezoensis thalli do not display extreme tolerance to high-light stress. In conclusion, our study reveals survival strategies of P. yezoensis against high-light stress, insighted into the ancient adaptation of intertidal red algae to the harsh environment.