To study the effects of ocean acidification and UV radiation on early life cycle stage of macroalgae, we selected the economic algae conchocelis of Pyropia haitanensis as our material. Two CO2 levels (ambient CO2, 390 ppmv and high CO2, 1000 ppmv) and three irradiances ( PAR (400-700nm), PA (315-400nm) and PAB (280-400nm)) were set in the study. Our results showed that high CO2 significantly enhanced the relative growth rate of conchocelis of Pyropia haitanensis, but the contents of phycoerythrin, phycocyanin, chlorophyll a, carotenoid and UVACs were significantly reduced by 7.3%, 9.3%, 19.8%, 16.5% and 18.7% under high CO2 condition, respectively. Maximum photochemical efficiency (Fv/Fm), light using efficiency (α) and maximum relative electron transport rate (rETRmax)were all significantly increased under high CO2 condition. When exposed to different light treatments, inhibition induced by PAR and PA were no significant differences between the thalli grown at high and ambient CO2. However, significant inhibition under PAB was found in the thalli grown at high CO2, which was closed related to the low concentration of UVACs in the thalli of conchocelis of Pyropia haitanensis. Inhibition induced by PAR were all lower than PA and PAB in both high and ambient CO2 treatments, however, no difference were found between PA and PAB treatments. In future ocean, increased UVR would show great effects on photosynthesis and growth of Pyropia haitanensis, especially under the background of ocean acidification.