The invention relates to a preparation method of thermotropic liquid crystal polyarylate. According to the invention, a prepolymer of the thermotropic liquid crystal polyarylate is prepared in a polymerization vessel through melt phase polycondensation, wherein the intrinsic viscosity of the prepolymer is 0.3-0.8 dl/g; the prepolymer is subjected to three processing stages which are preheating, low-temperature low-vacuum tackifying, and high-temperature high-vacuum tackifying, such that the thermotropic liquid crystal polyarylate with high molecular weight is prepared, wherein the intrinsic viscosity of the thermotropic liquid crystal polyarylate is 2.0-4.5 dl/g, and a molecular weight is 2.8*10<4> to 6.2*10<4>. The operation of the method is simple, and reaction conditions are easy to control. The prepared thermotropic liquid crystal polyarylate has high molecular weight, and can be prepared through continuous production. Therefore, defects of complicated steps, hard-to-control conditions, and unstable product qualities of traditional thermotropic liquid crystal polyarylate preparation methods are solved.