HgCdTe APD is one of the developing trends of third generation inferred FPA detectors. This article presents a new method to fabricate HgCdTe APD by Ion Beam Etch (IBE), and discusses the relation of gain to cutoff wavelength and depletion region thickness. A gain of 1000 at a bias of 17V was achieved in a HgCdTe APD with a cutoff wavelength of 4.8μm fabricated by this method. The noise factor, F, is calculated after a noise spectrum test.