Abstract: The temperature and light intensity vary greatly in Pyropia/Porphyra culture areas and the yield of Py. haitanensis is determined by the tolerant ability of high temperature and high light intensity. We studied the response of photosynthesis and growth of Py. haitanensis to different temperature and light intensity by laboratory culture in order to know whether ocean acidification (OA) change the temperature and light tolerance of Py. haitanensis. The results showed that both short-term (4 hours) and long-term (3-6 days) high temperature and high light intensity treatments increased the photosynthetic rate and growth rate of Py. haitanensis. Though 6 days of high temperature (31 ℃) treatment resulted in the death of thallus in particular, the OA treated thallus grew well with a growth rate of 0.1 d^-1. In the light range of 40-550 mmol/(m²·s), the growth rates of OA treated thallus increased by more than 27%. Our results indicate that OA can improve the high temperature and light intensity tolerances of Py. haitanensis and the Py. haitanensis cultivation industry may benefit from OA in the future.