There exist large quantities of engineering obstacles such as magnetic pole in some shallow water areas. In the light of the characteristics of magnetic pole, this paper, starting with an analysis of the magnetic field of the simplified mathematical model for the direct axis magnetized infinite extension columnar body, deals with the distribution regularity of the magnetic field and gradient field of the direct axis magnetized finite extension columnar magnetic body which is closer to the actual situation. On such a basis, it is suggested that the method of horizontal magnetic gradient measurement could be adopted to detect magnetic characteristics of magnetic pole.