The invention belongs to the technical field of water treatment, and in particular relates to a preparation method and application of a catalyst for removing trace hard-degraded organic matters in waste water. The catalyst is prepared by modifying a hollow magnetic nanomaterial by using copper and rare earth metals. The catalyst is found to be capable of efficiently carrying out catalytic oxidation on the trace hard-degraded organic matters in the waste water in a selective way in a waste water treatment and purification technology. The catalyst prepared by the method has the characteristics of being capable of being in full contact with reaction liquid, high in selectivity and activity, stable in performance, long in service life and easy to recycle.