Using the X-ray diffraction method, we have investigated the effects of high pressure and H+ impregnation on β→α transition in β-LiIO3 crystals. The samples had been subjected to high pressure treatment (up to 80kb)at room temperature and then preserved in ordinary environmental condition for different periods of time. The experimental results show that in β→α transition in the samples treated as above the pressure can be understood to play a role of promoting the nucleation of a -phase in β-matrix, and the pressure dependence of the rate of nucleation N can be expressed in the form of N ∝ekp (k= 26.8/bar). The significant increase of quantity of α-phase in such samples may be attributed to the rapid growth of α-LiIO3 nucleus under the influenle of H+ formed through the dissociation of adsorped water molecules on the surface of a nucleus. This conclusion is supported by the similar effects in the experiment of H+ impregnation of pressurized β-LiIO3 samples.