This paper describes the basic principle of Equivalent Offset Migration and Non-Imaging Shot-Record Migration. They both replace the usual offset coordinate with a new offset variable. The result of prestack time migration is followed by NMO and stack over the hyperbolic traveltime curve defined by the new offset variable. It is realized that prestack time migration is diffraction summation over the traveltime surface described by the double square root equation. The difference between the two methods is that they define different summation paths over the traveltime surface. The two methods can used to seismic imaging in the metal ores exploration.