The use of satellite images to quickly and accurately extract the distribution of the earth′s surface water body has been an important research topic all the time, which has important significance for water disaster monitoring, water resource utilization, etc. The operational land imager (OLI) remote sensing imagery is used to obtain the surface reflectance values of the images by radiometric calibration and atmospheric correction. Then principal components water index (PCWI) is constructed by analyzing the construction method of the typical water index and the principal component space features of ground objects. Taking Poyang Lake as the research area, two different time OLI images are selected during the dry season to extract water body information by using PCWI. The overall accuracy is 95.92% and 95.52% respectively. Compared with the water body extraction effects of other existing five typical water index, the overall effect of water extraction based on PCWI for the two different time OLI images is the best. In conclusion, PCWI of water extraction is feasible and effective.