When a formation of unmanned aerial vehicles(UAV) is used to localize a fixed target on the ground using time
difference of arrival, in order to improve the localization accuracy, an improved method based on the constrained total least squares(CTLS) and a method based on the structured total least norm(STLN) are proposed. Both methods are proved to have the same positioning accuracy, but the computational performance of STLN method is superior to CTLS method. Simulation results show that the proposed methods have high accuracy in position estimation.