Abstract: For the constant false alarm rate (CFAR) detection problem of active sonar in complex environment and propagation channel, an automatic CFAR detection method of active sonar based on hierarchical filters was proposed. Firstly, based on the spatial response characteristics of the array and the morphological characteristics of the target echo, a spatio-temporal filter was designed to remove the background noise and reverberation signal. Then, a linear and nonlinear combined spatial filter were designed to extract the energy accumulation area of the active sonar sonogram. Finally, the multidimensional features such as the spatial azimuth distribution of the target echo, the shape matching and the signal-to-noise ratio between the accumulation point and the adjacent background were calculated and fused to realize the target detection. Numerical simulation and sea test data show that, the probability of automatically detecting targets by this algorithm is larger than 85% in three typical cases, and this algorithm can detect targets when the background noise fluctuates greatly, showing that the algorithm is more robust.