Two spieces of Acropora corals (A. pulchra and A. millepora)were used to study the effects of phosphate stress on the photosynthesis of symbiotic algae. The Fv/Fm of the symbiotic algae was stable at the control level of phosphate concentration, but was depressed at under 15μmol/L and 30μmol/L of phosphate during the initial culture state compared with the control, and then increased after 2 and 5 days respectively,but to lower levels than that of the control. The density of the symbiotic algae at 15μmol/L and 30μmol/L concentration 5.59% and 14.69%. The symbiotic algae of A. pulchra and A. millepora were able tolerate phosphate concentration <30 μmol/L, but their Fv/Fm and density were reduced significantly.