The detecting depth and depth estimation of natural-source frequency electromagnetic sounding are firstly analyzed in this paper. Then the detecting depth and depth estimation of artificial-source frequency electro-magnetic sounding is discussed. Compared with the natural source frequency electromagnetic sounding, the artificial-source frequency electromagnetic sounding has additional offset distance effect, its depth estimation should be experiential. The detecting depth and evaluation method of the frequency electromagnetic sounding is theoretically focused and can be used to guide the operation design or semi-quantitative interpretation. More accurate detecting depth of frequency electromagnetic sounding was obtained through the correct inversion and interpretation.