Abstract: Dealing with the problem of positioning a moving object by a long-base line acoustic tracking system,it is needed to solve the nonlinear equations,whose solution has already been known in the literature.In this article,an approximate solution of the positioning equations is put forwards and it shows the benefits of simpler computation and fewer transponders needed.In stead of the complex nonlinear equations,the presented method only needs to deal with the familiar circular equations,which are simpler than the original ones.Both the computer simulations and marine experiments show that the method presented not only is simple enough,but also meets with the attractive precission.