Abstract: The paper discusses how to apply methods of target motion analysis on bearings-only estimation of underwater target motion parameters. In the aspect of target motion analysis, bearings-only estimation of target motion parameters is the most difficult one with vast application area. As bearingsonly target motion analysis is a problem of extreme nonlinearity, most estimation methods based on linear models have been proved their unproperiety for the solution of the problem, especially when the noise of target bearing observation goes up. It is difficult for most estimation method to provide unbiased result for the solution of the problem. We use Generalized-Least-Square method on the rough estimation of target motion parameters, then use Sequential Uniform Design method to raise a more preciseestimation on the basis of rough estimation. Algorithm based on these two methods has proved its goodproperiety on bearings-only target motion analysis even under conditions of large bearing obesrvationerror.