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We demonstrate an efficient and convenient method to recognize the orientation of fluorescent molecules through back focus imaging technology in leakage radiation microscopy. In the common structure of this microscope, the resonant energy transfer from a fluorescent emitter will be modulated and coupled into various waveguide modes. The specific intensity and angular distribution of all modes can be obtained clearly from the back focal plane. This energy transfer is strongly distance-dependent and the axial distribution information can be uniquely determined through the intensity ratio of transverse electric modes. When using the intensity ratio between transverse magnetic modes simultaneity, we find that the three-dimensional spatial orientations of the fluorescent molecules can be obtained directly.