The invention relates to a dismantling method for resisting an impact load in the high-altitude overhanging steel-structure-platform dismantling process. The dismantling method is characterized by including the following steps that 1, the cutting position of a steel truss is determined, a slotting line is drawn up, the steel truss is divided into two parts, one part is a fixing-section steel truss body connected with a concrete body structure, and the other part is a lifting-section steel truss body far away from the concrete body structure; 2, an outer-side lifting point of the lifting-section steel truss body and a structural tower lifting hook are fixed, a lifting rope is frapped, an inner-side lifting point of the lifting-section steel truss body is fixed through an inner-side lifting-device lifting hook, and the lifting rope is frapped; 3, an auxiliary hanging plate stretches across the slotting line, is fixed at the upper portion of the steel truss and fixedly connected with the lifting-section steel truss body, and is not connected with the fixing-section steel truss body; 4, the steel truss is cut off in the slotting line, then the lifting-section steel truss body is lifted through the inner-side lifting point and the outer-side lifting point of the lifting-section steel truss body, and the lifting-section steel truss body is dismantled. According to the dismantling method, the construction cost is low, and the impact load in the dismantling process can be resisted.