In order to quantitatively analyse the impact of thermal discharge on 〖WTBX〗Coscinodiscus Jonesianus〖WTBZ〗 biomass at different temperature rise gradient. A three dimensional hydrodynamic model was set up to simulate the distribution characteristics, impact area and volume of thermal discharge at different temperature gradient in the summer of 2011 with FVCOM model, and based on the experiment data of enclosure experiments in Xiangshan Bay in summer of 2011, the losses of 〖WTBX〗Coscinodiscus Jonesianus〖WTBZ〗 biomass at different temperature gradient ranges were analysed. The results showed that the surface temperature rise range in summer was mainly distributed within the envelope of 1.5 centigrade temperature rise, while the bottom one was within the envelope of 1.0 centigrade temperature rise. The seawater volume affected by weak temperature rise zone and strong temperature rise zone were 93.650 million m3 and 1.073 million m3 respectively, with a total of 94.723 million m3. The total losses of 〖WTBX〗Coscinodiscus Jonesianus〖WTBZ〗 biomass influenced by the thermal discharge were 32.580 trillion cells , and the weak temperature rise zone accounted for 94.76 percent, while the strong temperature rise zone was only 5.24 percent.