Abstract: The sensitive grain-size component is one of the important approaches to analyze sedimentary environment change. Tidal flat around Qidong cape is located at the intersection between the coast of Jiangsu and the river line of the Yangtze River, where with intense land-sea interactivities. With economic development, the area is affected by human activities heavily. Four cores are collected during field investigation. After grain size analysis, the sensitive grain-size components are identified based on standard deviation. The results are as follows: (1) there is a distinct negative correlation between fine components and coarse components. The fine components of <22 μm, <26 μm, <22 μm in the core QDZ-1, QDZ-2 and QDZ-3 sediments gradually increases from bottom to top, which could reflect general law of tidal flat sedimentation. (2) The coarse components suddenly increase under the influence of extreme environmental changes such as floods and storm surges. The coarse components of >22 μm, >26 μm and >22 μm in the core QDZ-1, QDZ-2 and QDZ-3 sediments increased sharply to 84%, 85% and 80% at depths of 172.5 cm, 242.5 cm and 142.5 cm respectively. (3) The fine components are more likely to leach than the coarse components under the influence of human activities, and as a result, that sediment tends to coarsen. The coarse components of >26 μm of QDZ-2 showed an increasing trend in the upper part of the section A. The reason is due to the combined effects of agricultural activities and rainwater leaching. The coarse components of 22 μm～88 μm and >88 μm of QDZ-3 show an increasing trend in the upper part of the section A. The coarse components of >63 μm of QDZ-4 showed the same. The reason is that the sedimentary dynamic enhanced by reclamation dikes constructed. As a result, coarse components are easier than fine components to adapt to high-energy environment and to deposit.