Abstract: This paper presents the theory of passive localization for underwater sources based on Acoustic Ray channel modelling.The principles of channel modelling in Ray-theory) determination of eigenrays which connect source and receiver,analysis of DOA arriving structure and time delay spectrum arriving structure,their relationship to source location are given in the paper.Source location is estimated by matching measured DOA and TDS to their calculated counterparts.The method of Ray-theory based passive localization features its simplicity,less calculation,short array aperture and robust performance to environment parameters,as compared with those methods based on Normal Mode theory.It is expected that this theory may find practical applications in the coming years.