Abstract: With the development of RS technology, there is an important significance for exploiting the marine resources reasonably and protecting the marine ecological environment by using remote sensing data to obtain the information of offshore aquaculture, and studying the effects of offshore aquaculture. Taking the adjacent waters of Yantai City, Shandong Province as the study area, according to the spectrum characteristics of the image, a water index was constructed to extract offshore aquaculture area firstly. Then, the deep water was extracted which had similar spectrum with aquaculture area. Finally, combining the results of the two operations, the aquaculture area was isolated from the deep water. Accuracy evaluation results show that the extracted aquaculture area by using this method and on-the-spot investigation results are basically the same. The overall accuracy reached 86.14%. Thus, this method can effectively provide information basis for the farming decision.