A synthesis method for low-transoleate content polysorbate 80 for injection, comprising the following synthesis steps : mixing polyoxyethylene (20) sorbitol anhydride and high-purity low-carbon oleic acid alcohol ester according to a certain ratio, performing transesterification reaction under the action of a catalyst and in vacuum, and then performing refinement, sterilization, and removal of a pyrogen to obtain the polysorbate 80 for injection. The mass ratio of the polyoxyethylene (20) sorbitol anhydride to the high-purity low-carbon oleic acid alcohol ester ranges from 1 : 0.3 to 1 : 0.5. Compared with other methods, the method has the advantages as follows : the reaction temperature is lowered, conversion between cis-trans isomers of the oleic acid is effectively inhibited, so that the content of transoleate in the polysorbate 80 is reduced to be lower than or equal to 0.3%, and the chroma (APHA) is reduced to be lower than or equal to 30, and the biosafety of the polysorbate 80 is improved, moreover, the process operations are simplified, the process production efficiency is improved, and the production costs are reduced.