The IP method is one of the important means of prospecting porphyry ore deposit, but for the reasons of shallower exploration depth, the interference of carbon and useless metal sulfide, etc, it is unable to locate or evaluate concealed deposit. This passage takes the concealed porphyry copper-molybdenum ore for example, based on analysis regional ore-forming geological setting, the IP work result of the predecessors, and rock physical characters, combining typical porphyry metallogenic model, puts forward the ideas that applying transient electromagnetic method towards delimitating controlling ore body, and the middle-high electromagnetic induction change rate regions of the top and marginal of rock mass is the metallogenic favored site.