简介了磁粉探伤中Betz环的两种近似理论，即等效(磁偶极矩、埋藏深度)近似和磁偶极子链近似。由磁偶极子链近似理论计算和画出了Betz环表面上显现出埋藏小孔磁痕的外加临界磁化电流与小孔数间的关系曲线，其中之一的趋势与实验曲线一致。同时证明了磁化电流无需饱和即可显现Betz环上12个孔。

Two types of approximate theories for Betzs ring in magnetic particle testing were briefly introduced, which were the approaching of equivalent magnetic dipole strengths and equivalent hole depths as well as the approaching of magnetic dipole chains. From the later, the characteristic curves between the number of small hole and the critical applied magnetizing current, by which the magnetic particle pattern of the buried hole were revealed on the ring circumference, were calculated and plotted. The tendency of one of these characteristics is identical with the experimental curves. And it was also proved that for the magnetizing electric current there is no need to reach saturation to reveal all twelve holes of Betzs ring.