Abstract: In order to understand the impact of macroscopic algae farming on seawater DO content, to clear the change process of DO content, in light, dark, light and dark alternately conditions, Sargassum thunbergii and Hizikia fusiforme from Wenzhou Dongtou offshore were brought to the laboratory for breeding. Set light (2h, 6h, 12h), dark (2h, 6h, 12h), alternating light and dark (1h 1h, 6h 6h, 12h 12h) treatment conditions, DO was determined, also to analyzed its oxygen production rate and oxygen consumption rate. The result showed that: with the extension of farming time, Sargassum thunbergii and Hizikia fusiforme oxygen production rates were all declining, Sargassum thunbergii oxygen production rate was higher than Hizikia fusiforme (P<0.05); Under dark conditions, Sargassum thunbergii maximum oxygen consumption rate at the time of 6h up to 288.02mg/kgDW?h, Hizikia fusiforme maximum oxygen consumption rate at the time of 2h up to 207.46 mg / kgDW?h, Sargassum thunbergii oxygen consumption rate was higher than Hizikia fusiforme; Sargassum thunbergii net oxygen production rate under alternating light and dark increased slowly at first and then drastically reduced, the net oxygen production rate up to 457.08 mg / kgDW?h at the short alternating cycle (1h 1h). Hizikia fusiforme net oxygen production rate first increased and then decreased, while the medium alternating cycle (6h 6h) up to 64.04 mg / kgDW?h. Macroscopic algae farming with alternating light and dark environment when carried out, photosynthetic oxygen production and dark respiration oxygen consumption converted continuously. Overall, Macroscopic algae farming increased the DO content of the seawater. Ecological and social value of the macroscopic algae farming was significantly, it should be vigorously promoted.