The daily course of photosynthesis of Bangia fusco-purpurea in situ was determined by using photosynthetic gas exchange and chlorophyll a fluorescence. The results showed that its photosynthetic rate and chlorophyll a florescence parameters in the emersed algae decreased quicker than that in the submersed algae in noon. When the emersed algae was resubmersed, all chlorophyll a fluorescence parameters could recover to the levels of the submersed algae in two hours, respectively. Insignificant fluctuation of chlorophyll a, carotenoid or phycoerythrin contents was observed in daytime. All above results suggested that the photoinhibition of Bangia fusco-purpurea in situ existed at noon, and the emersed algae exhibited photoinhibition more severe than the submersed algae. The photosynthesis in both submersed and emersed algae could be recovered in evening. The reaction centers of PSⅡin Bangia fusco-purpurea could developed some strategies which contained the increase of thermal dissipation and the reduction of electron transport rate to resist photoinhibition.