Abstract: Since the most of existing algorithms of direction of arrival (DOA) have spatial ambiguity to the signals which are mirror symmetry to x axis, T shape array is usually used to overcome the spatial ambiguity. In this paper, a new DOA estimation method based on train signal is proposed. The new method is based on the supposition:the training signals are mutually orthogonal and the magnitude of each signal is constant. The paper gives out the mathematical derivation of the new algorithm and gets a simple estimating formula. The simulation result shows that the new algorithm can estimate the DOA accurately and rapidly.