Abstract: Ray tracing method is usually used for determining depth and plan position in multibeam swath bathymetry.Sound speed profile or sound speed function must be used in the practical calculate procedure with ray tracing method.However,the method shows complicated,loaded down with trivial details and time-consuming.In order to improve the situation,a new method is presented for depth and plan position estimate in this paper.The method is divided into two situa-tions.One is that sound speed propagation is considered to keep to constant gradient change in whole propagation procedure,and the other is that sound speed change is regarded to follow different constant gradient in different water layer included in whole transmitting water columns.For the former,the sound speed profile or sound speed function is needed in practical application,and the parameters of surface incidence and sound speed in bottom only are required in the calculating procedure.At the same time,the estimating accuracy is much less than the IHO standard of 1% depth when water depth is deeper than 30m.For the latter,some ways in tracing ray method are adopted in data processing,but the division layer is different from that in ray tracing method.The division of all propagation time is adopted in the new method.Because some similar ways in ray tracing are used,the accuracy of method determining depth and plan position should be on the same level as ray tracing method.Of course,its accuracy is affected by division layer that is like the other diversion layer method.If the sound speed profile is strictly referenced in defining time layer,the calculating accuracy should be ensured.Otherwise,it is difficultly ensured.The processing procedure of the second situation is easier than the ray tracing method.The new method is very useful for precise determining depth and plan position,its calculating processing is very simple and easy,its estimating accuracy is the same to or near that of the ray tracing method.