Abstract: The pressure and particle velocity combined processing technology based on an acoustic vector-sensor is applied to the passive direction estimation for low altitude targets. The procedure of the proposed approach is given, followed by the experimental investigations with the noise data radiated by a helicopter. The influence of the size of vector-sensor, time of integration and SNR (Signal-to-Noise Ratio) on the accuracy of direction estimation is analyzed, respectively. It is shown that the direction estimation error of lower than 2 degrees can be achieved, with the vector-sensor size 0.2 m and SNR 0 dB. This research provides a, feasible approach for accurately passive acoustic detection for low altitude targets with a smaller array.