In order to improve the early warning success rate of underwater magnetic targets, a magnetic target detection method based on array vector magnetometer is designed. According to the combination of theoretical derivation and simulation, the magnetic anomaly signal characteristics of the magnetic target in the array coordinate system are analyzed, and the target distance calculation method is deduced. Taking typical magnetic target as the detection object, the magnetic anomaly characteristics of the target movement are simulated and obtained the relationship between array spacing and detection distance. The simulation results show that the design has a certain practicability and can provide a reference for the early warning of underwater magnetic targets in specific sea areas.