To solve the problem of the uncertainty of the searching width of the magnetic anomaly detector caused by the uncertain diving depth of the enemy submarine in practical combat, the concept of average searching width is put forward and the calculation model of the average searching width of the magnetic anomaly detector is built based on the performance characteristics of the magnetic anomaly detectorswhich can provide the basic parameters for combat plan and preparation. Two types, totally three kinds of searching methods are proposed for the anti-submarine patrol aircraft to carry out regional search with the magnetic anomaly detector. Two types, totally four kinds of action plans for use after the contact are given. The model is proposed for calculating the probability of successfully detecting the enemy submarines in specified areas by the anti-submarine patrol aircraft with the magnetic anomaly detector, and this model can be applied to inverse calculation.