Abstract: Based on the calculation of MODIS data RVI in areas of the Yellow Sea and the East China Sea during the period of 2008~2015, the information about spatial distribution characteristics in the initial stage of Ulva. Prolifera, drift paths, spatial distribution and aggregation degree of variation were obtained using threshold segmentation method and ArcGIS spatial analysis technology.The results showed that:1) Ulva. Prolifera generated firstly in the mid May and the early June and mainly located in the sea areas near north of Yancheng (Jiangsu Province) and the Yangtze river estuary. 2) With the growth and outbreak of Ulva. Prolifera, it drifted to the northwest till the offshore waters of north Jiangsu, and then into the Yellow Sea. The drift paths had obvious interannual variation characteristics. 3) During the growth, the spatial distribution characteristics of Ulva. Prolifera usually displayed a growing tendency from south to north with aggregating and expanding, while wholly drifting phenomenon occurs at times. 4) Entering the period of treatment, the coverage density of Ulva. Prolifera began to decrease until it disappeared completely. This research is contributed to the understanding of occurrence and development characteristics of Ulva. Prolifera disaster and provide technical support for the further effective management.