用磁偶极子模型分析了方钢表面矩形贯通沟槽的深度d与该沟槽引起漏磁场H间的关系，推知：1）当d很小时，H∝d；2）d较大时，H∝(d-2kδ)(δ是d的函数，k为比例系数)；3）当d很大时，随着d的增加，H反而减小。推论1）和2）都早已为磁粉探伤的经典试验所验证，推论3）因未见现有文献记载，故尚待实验验证。此外，还给出了H-d的5种近似解析表达式。

The relation of the depth d of a rectangular through slot on the surface of a cuboid steel component and the magnetic leakage field H caused by the slot is analyzed by the model of magnetic dipole in the present paper. It is deduced, that 1) when d is very small, H∝d; 2) when d is larger, H∝(d-2kδ)(δ is a function of d, k is a coefficient); 3) when d is very large, on the contrary, H will decrease with the increasing of d. The inferences 1) and 2) have already been verified long ago by the classical experiments in magnetic particle inspection. And the inference 3) has never been seen in now available references, so it remains to be verified by experiment. Besides, five approximate analytical expressions between H and d are given.