Abstract: In situ winter Chlorophyll a data in Changjiang Estuary and the adjacent sea were compared with the active fluorescence data and remote sensing data, in order to analyze the distribution of chlorophyll a in winter and the potential applications of active fluorometer and remote sensing technology. The result shows that the mean chlorophyll a concentration of the investigate area in winter is approximately 0.85 mg/m3 with a high value zone (1.30 mg/m3) located at southeast of Changjiang Estuary. What's more, the value of the maximal fluorescence Fm and minimal fluorescence Fo measured by PhytoFlash submersible active fluorometer can give a very accurate depiction of the real surface distribution of chlorophyll a. Distribution of the maximal quantum yield (Fv/Fm) can be used to evaluate the responses of phytoplankton to different limiting factors such as nutrient, temperature and light, etc. In addition, though the average of chlorophyll a retrieved by remote sensing data (0.94 mg/m3) is a little higher than the measured value, it still has the practical value to reflect the real trend of chlorophyll a distribution.