The invention relates to a method for preparing polyester fibers with ultraviolet-resistant and anti-pilling composite function. The method comprises an esterification reaction procedure, a polymerization reaction procedure and a spinning procedure, wherein the esterification reaction procedure comprises a primary esterification reaction stage and a secondary esterification reaction stage, and aliphatic dicarboxylic acid or non-p-aryl dicarboxylic acid serving as a third monomer is introduced in the primary esterification reaction stage; flexible polyethylene glycol serving as a fourth monomer is introduced in the secondary esterification reaction stage; a hindered amine light stabilizer and a hindered phenol antioxidant which are respectively prepared by using acetic acid and ethylene glycol as solvents and hydroxy silicone oil are added after the esterification is completed; and after the pre-polymerization of the polymerization reaction procedure is completed and before final polymerization, an ultraviolet absorbent is added. Before the spinning procedure, polyester slices are pre-crystallized and dried. The polyester fibers obtained by the method have excellent ultraviolet-resistant and anti-pilling function; and after the polyester fibers are woven into knitted fabrics and woven fabrics, tests show the related technical indexes that: the ultraviolet transmission rate is less than or equal to 5.0 percent, and the anti-pilling performance is more than or equal to level 4.