Growth and photosynthesis characteristics of high temperature tolerant macroalga, Gracilaria lemaneiformis, were studied at different temperature and light irradiance. Nutrient uptake rate and nutrient reduction efficiency of ammonium and phosphorus from scallop excretion were determined. Temperature significantly affected the growth and photosynthesis of this species. The algae could grow well when the temperature ranged 15℃ and 25℃, and reached the fastest growth rate (SGR) of 2.8% per day at 20℃. The photosynthetic rate increased with the increasing temperature and light irradiance, reaching the maximum with 5.0 mg O2/(g dw•h) at 30℃ and 120 μmol/(m^２•s). G. lemaneiformis can absorb efficiently the ammonium and phosphorus from scallop excretion. The nutrient uptake rate and nutrient reduction efficiency of ammonium and phosphorus changed with cultivation density and period. The maximum reduction efficiency of ammonium and phosphorus were 83.7 and 70.4 percent, respectively. The maximum uptake rate of ammonium and phosphorus were 9.9 μmol/(g ww•h) and 4.3 μmol/(g ww•h). Results indicated that this seaweed can be cultivated in north China and is a suitable candidate for integrated mariculture of seaweed and bivalve. The integration can benefit economy and environment in a sustainable manner in warm seasons in coastal waters of north China.