The invention discloses a preparation method of master batch for PBT fibers. The master batch is prepared from the following components in parts by weight: 23 parts of PBT, 12 parts of pigments, 1.4 parts of cobalt naphthenate, 2.3 parts of aminotriacetic acid, 3.1 parts of sulfamic acid, 0.8 part of zinc dihydrogen phosphate, 1.5 parts of sodium fluosilicate, 2.6 parts of polyoxyethylene oleate,0.9 part of alkyl aryl sodium sulfonate, 1.1 parts of sodium persulfate, 2.3 parts of nonylphenol ethoxylate carboxylate, and 1.9 parts of N-methyl pyrrolidone. The master batch prepared by the invention is suitable for the PBT fibers, and the master batch is good in ultraviolet resistance.