To meet realtime processing, a new direction finding algorithm is proposed for reducing the huge computation of traditional MUSIC algorithm in DOA estimation. Based on the orthogonal of signal and noise subspace, this algorithm uses the partial noise subspace to search the spectrum peak with variable stepping. It substantially lowers the implementation complexity by reducing the calculation of single pseudo spectrum and spectrum searching range, avoiding signal number estimation, and optimizes addition and multiplication operation for less than a quarter computations. The new DOA algorithm can realize realtime signal processing with less operation load. The performance is proved through modeling, simulation and comparison.