The invention belongs to the field of constructional engineering and in particular relates to a high-precision method and structure for positioning a high-precision precast beam. The method comprises the following steps: installing at least one stop pin on the bottom of the end part of a precast beam; installing one locating rack on one side surface, opposite to the other beam column, of at leastone beam column, wherein the locating rack is provided with a locating plate; the locating plate is horizontally extended and arranged and is provided with a locating hole; the precast beam is hoisted above the beam column; the horizontal position of the precast beam is adjusted to cause the stop pin to correspond to the locating hole; the precast beam is fallen to cause the precast beam to be arranged on the upper end of the beam column; and the stop pin is inserted in the locating hole. The method has the advantages of high positioning precision during installation, simplicity and convenience in construction and capability of greatly saving the days for construction, manpower and material resources; and the structure provided by the invention is stable, and the positioning tool is simple in structure, can be reused and is low in cost.