The invention relates to a laser annealing device comprising a wafer stage, a first energy detector, a second energy detector, a third energy detector, a spatial light modulator, an energy absorption unit, a system controller, and a wafer stage controller, a reflectivity measurement unit and an energy modulation annealing unit which are connected with the system controller. The wafer stage controller is connected with the wafer stage, and controls movement of the wafer stage. One part of laser emitted by the reflectivity measurement unit enters the first energy detector, and the other part is transmitted to the surface of a wafer, reflected by the surface of the wafer and transmitted to the second energy detector. The reflectivity of the wafer is obtained according to the values of the first energy detector and the second energy detector. One part of laser emitted by the energy modulation annealing unit enters the third energy detector, and the other part is transmitted to the surface of the wafer via the spatial light modulator, reflected by the surface of the wafer and transmitted to the energy absorption unit. The value of reflectivity of the wafer obtained is input to the input end of the spatial light modulator.