Abstract: The Rotating Magnet Ranging System is a new technique for accurately detecting the distance between adjacent wells, and it is taking more and more important roles in drilling wells with complex structure. The equivalent magnetic moment of the magnetic sub is one of the important indicators for assessing the measurement reliability, and the measurement of the equivalent magnetic moment is one of the key parts during the working of Rotating Magnetic Ranging System. On the basis of the magnetic field distribution around the magnetic dipole, the far-field magnetic field distribution around the rotating magnetic sub is derived. The discontinuous measurement method and the continuous measurement method for magnetic sub equivalent moment are obtained, and the complexity and factors affecting measurement accuracy of the two measurement methods are preliminarily discussed. The result indicates that the continuous measurement method for magnetic sub equivalent moment is easier to handle and has less influence factors and a higher precision, so it is easier to be practically applied than the discontinuous measurement method.