Abstract: A new approach to coastal water quality analysis is expected in this paper through the study on the SOM(Self Or ganizing Map).Firstly,the water quality data of Bohai Bay is ready. Then,a set of software for coastal water quality analysis is developed based on the batch version algorism of the SOM and the SOM toolbox in the MATLAB environment. This software can analyze and display the data charact ers through the training of the SOM. Furthermore,the training results can be analyzed so that the data is divided to five different kinds of pollution. Lastly,it is also realized that the monitored data serial can be tracked,and the new data can be classified automatically. Through application it can be found that this study helps to analyze the coastal water quality in depth with several kinds of graphics,which supply the decision support to recognize the pollution status and takeing the corresponding measures.