Abstract: This paper discusses the high precision locating problem of dot target in near field by using the technique of focusing beam forming with linear array. The effect of multi-path and fluctuates of sea surface are analyzed. By the beam leading the computations for scanning is reduced,and by using the methods of virtual array,time reverse mirror and product of sound-map,the "brightness" of focusing and the quality of sound-map are improved. The result of simulating tests show that the methods of virtual array and time reverse mirror can restrain the interference brought by multi-path,and that the app-lication of the product of sound-map makes the target dot clearer. The target can be easily detected when the SNR is as low as 0db.