The invention relates to a preparation method of perovskite-structure relaxor ferroelectric single crystal lead indium niobate-lead magnesium niobate-lead titanate. The chemical composition of the perovskite-structure relaxor ferroelectric single crystal lead indium niobate-lead magnesium niobate-lead titanate is (1-x-y)Pb(In1/2Nb1/2)O3-yPb(Mg1/3Nb2/3)O3-xPbTiO3, wherein x is equal to 0.20-0.45 and y is equal to 0.15-0.70. The preparation method comprises the following steps: (1) preparing a primary crystal growth raw material; (2) primarily growing crystals; (3) preparing secondary crystal growth raw material; and (4) secondarily growing the crystals. According to the preparation method disclosed by the invention, a crucible descending multi-growth method is adopted, the component segregation of wafers can be obviously suppressed, the high-performance areas of the crystals can be expanded, and relaxor ferroelectric single crystal material PIMNT with large dimensions, large high-performance intervals and high quality can be grown effectively with regard to the optimally-orientated wafers for different applications, thus the utilization rate of the crystals is increased, and the difficulties of batch growth and applications of single crystals can be overcome.