Abstract: Extent of inundation is a key factor in flood damage assessment. In the previous research on flood damage assessment, flooded regions were often assigned weight coefficients corresponding to the submerged acreage, which actually implied that equal weighting of flooded acreage factor was used in flood damage assessment. However, extent of inundation usually changed during a flood event.For example, one spot may be submerged at the beginning of flooding and then may become non-flooded soon afterwards, while other areas may be submerged for the whole period of a flooding event. Therefore, these areas should be assigned time-weighted inundated acreage to take into account of their differences in inundation duration. Based on this fact, Variation Index of Flood (VIF) and Comparison Index of Flood Disaster (CIFD) were proposed to monitor the spatio-temporal characteristics of 2016 summer flood in the Poyang Lake regions. In order to acquire the actual acreage factor, the extent of inundation from 23rd to June 25th of July was mapped using GPS-based field investigation and remote sensing data before and after the flooding, including multi-temporal Landsat 8 OLI, GF-1 WFV and Google earth imagery. To resolve the difficulty in remote sensing distinction between water body and the flooded area, image fusion was applied to integrate information from Normalized Difference Vegetation Index, Modified Normalized Difference Water Index (MNDWI) of the Landsat 8 OLI in the early stage of the flood event and Normalized Difference Water Index (NDVI) in the latter stage. By doing so, the color differences between water body and the flooded area in the satellite images can be enlarged to have an effective discrimination of these areas. This study revealed that: 1) A total area of 33 329.28 hm2 was covered by flood excluding the original extent of the water in the study area. And 81% of flooded land area occurred in counties of Poyang, Yongxiu, Yugan, Duchang, Xinjian, Xingzi and Jinxian,located in the lake region; 2) VIF tnder decreased from 3.75 in early stage to 1.29 in later stage, implying that the flood damage diminish quickly during that flood event;3) The most severe flood damage was in Poyang County with the CIFD index of 1.954, the largest among all other counties;4) Although the proposed method needs further testing, our investigation demonstrated the feasibility and the usefulness of the combined use of VIF and CIFD models and the image fusion processing technique to integrate NDVI, NDWI and MNDWI at the differentflooding stages in the flood damage assessment procedure.