Abstract: This paper studies the response of phytoplankton cell density to environmental factors in the Yueqing bay based on the survey data of the Yueqing bay in May 2004.This study analyses the ecological threshold of phytoplankton density under the salinity environment gradient using the Gaussian model.The results show that the optimum salinity of phytoplankton growth is 26.12, the ecological threshold of salinity is24.36, 27.88, the optimum ecological threshold is25.24, 27.00, the corresponding salinity is 26.48 at the maximum cell density in the measured data, and it is within the range of optimum ecological threshold.It can provide the best reference value and early warning threshold for the sustainability of the marine ecosystem for the monitoring and early warning of the resources and environment carrying capacity of the sea area, and build an early-warning model for carrying capacity of marine resources and environment.