The invention discloses a method for preparing a special compatibilizer PBS-g-MAH for a straw fiber/poly(butylene succinate) (PBS) composite material and application of the compatibilizer in the straw fiber/PBS composite material. The prepared special compatibilizer is a grafted copolymer, PBS and maleic anhydride (MAH) are melted and blended by using a double-screw extruder, and then the PBS-g-MAH is prepared by adopting a radiation grafting method. The radiation grafting method is high in grafting efficiency, the grafting rate of the prepared PBS-g-MAH is high, and the interfacial compatibility of straw fibers and the PBS can be greatly improved. When the PBS-g-MAH is applied to a straw fiber/ PBS blended system, the carboxy included in the PBS-g-MAH and the hydroxy of the straw fibers undergo esterification reaction, so that the polarity and water absorption of the straw fibers are reduced; meanwhile, the long chain of the graft can be inserted into a PBS matrix and plays a role of a bridge between the PBS and the straw fibers, so that the interfacial compatibility of the straw fibers and the PBS is greatly improved.