Abstract: Seagrass bed is an ecosystem with high productivity, and it is an important spawning ground and nursery for many marine aquatic organisms in coastal waters. The temporal and spatial variation characteristics of environmental factors such as PFD, Temp, SPM, POM and Chl a were monitored and analyzed through the annual survey in seagrass bed and its adjacent bare sand area in Swan lake, Shandong province. The result showed that seagrass bed has a strong regulating effect on temperature and light. The temperature of the seagrass bed was higher than that of the bare sand area, accounting for 58.7% of the spring and autumn. The temperature of the seagrass bed was lower than that of the bare sand area, accounting for 94.2% of the summer. The PFD of seagrass bed was significantly lower than that of bare sand area, and the average was 60.3% of that of bare sand area in spring and summer. Both shoot density and shoot height had significant effects on light and water temperature, which had significant negative correlation with DTA and PFD of seagrass bed. The result indicate that seagrass bed has an obvious shading effect, 'cooling' in summer and 'warming' in spring and autumn, which provides a good environmental basis for the conservation of biological resources.