Magnetic anomaly detection(MAD)is an important detection technology in the field of covert target detection. The progress of magnetic sensor technology makes vector magnetic detection become a hot spot all over the world. However,there are few discussions about quantitative detection methods of vector magnetic anomaly,and there still is a huge debate on the differences between vector magnetic detection and scalar detection. In this paper,a covert target detection method based on 3D imaging of vector magnetic anomaly is applied to discuss the differences between scalar magnetic detection and vector magnetic detection. The detection efficiency of vector magnetic anomaly is discussed through simulation experiments and field application. The study shows that 3D imaging of vector magnetic anomaly can detect 3D spatial distribution and magnetic characteristics of covert targets more accurately,which can provide a powerful strategy for target location and identification.