The invention relates to a method for preparing magnesium calcined dolomite by a microwave fluidized bed furnace controlled by a microcomputer. In the method, dolomite is taken as a raw material, and is calcined in the microwave fluidized bed furnace at a temperature of 1,030 DEG C, a sensor controls and display temperature information, the material is charged by a screw feeder, the product is collected by a cyclone dust collector, the tail gas CO2 is collected by a bag filter dust collector, the water circulation condensing method is utilized for recovery, and the inside-furnace temperature, the microwave heating, the compression air speed, the heating time, the cyclone dust collection and the bag dust collection are all controlled by microcomputer program; for the prepared magnesium calcined dolomite, the burn rate is 47 percent, the ignition loss is less than or equal to 0.5 percent, the activity degree is more than 34 percent, and the magnesia content of the product is between 38 and 44 percent; and the preparation process flow is short, the boiling calcining is fast, the calcining time is 15 seconds, and the cycle of feeding, calcining and discharging is 5 minutes; the microwave heating speed is quick, and the efficiency is high; and compared with the prior art, the efficiency is improved by 2 to 3 times, so that the energy is saved, the environmental pollution is reduced, and the method is a quite ideal method for preparing the magnesium calcined dolomite.