Abstract: CBF（Conventional Beam Forming） array processing is the optimal detecting system while only one target presented in omni-directional ambient noise.However,its performances degrade in complex condition of multi-target interferes.Base on the character that the radiated noise of passive target contains high intensive and stable line spectrum, the paper puts forward CBF Variance-of-Frequency Detector,which weighs bearing spectrum using the variance of peak frequency of each azimuth.It is able to suppress multi-target interferes effectively,and detect faint signal in the background of strong interferes.What’s more,CBF Variance-of-Frequency Detector only needs three-dimensional display,while other line-spectrum detectors require for four-dimensional.The simulation and trial results show that the CBF Variance-of-Frequency Detector is able to detect line-spectrum target in the background of multitudinous and strong interferes.