The invention belongs to the field of piezoelectric ceramic materials, and particularly relates to a preparation method of bismuth ferrite-lead titanate-bismuth magnesium niobate ternary system high-temperature piezoelectric ceramic. The chemical formula is (1-x-y) BiFeO3-xPbTiO3-yBi (Mg2 / 3Nb1 / 3) O3, x and y are molar weights, and x is more than or equal to 0.20 and less than or equal to 0.40; 0.01 < = y < = 0.10; the auxiliary component is mBi2O3 + nPbO + zMnO, m, n and z are the mass percent of the total formula, and m is larger than or equal to 0 and smaller than or equal to 0.10; 0 < = n < = 0.10; 0 < = z < = 0.10. The preparation method comprises the following steps: S1, weighing the raw materials; s2, carrying out primary ball milling; step S3: drying; s4, performing solid-phase synthesis; step S5, carrying out secondary ball milling; step S6, granulating and forming; step S7, glue discharging; step S8; and step S9. The sintering temperature of a system can be reduced, ceramic densification is promoted, cracking and pulverization are avoided, the ceramic has the good sintering characteristic, the c / a ratio of the system is reduced, the material is easy to polarize, the ceramic obtains the large piezoelectric coefficient under the condition that the high Curie temperature is guaranteed, the insulativity and temperature stability of the material are improved, and the service life of the material is prolonged. And practical application of devices at high temperature is facilitated.