Abstract: A classification method based on the concept of phase-plane traces is presented for distinguishing seabed types. The essential part of the method is the phase-plane traces analysis of seabed echosound data. Two characteristic parameters can be extracted from the traces:one is the maximal distance parameter, the another is the distance distribution parameter. The method was used to process sea survey data got from two similar seabed types, and easily distinguished them. The results show that the method can be used to classify the seabed types.