The invention relates to the technical field of metallurgy and particularly relates to a production method of light calcined magnesia. The production method of the light calcined magnesia comprises the following steps: by adopting magnesite of which the particle size is smaller than 30mm as a raw material, conveying the magnesite to a rotary microwave roaster and mixing with recrystallized silicon carbide spheres; indirectly heating the magnesite to produce the light calcined magnesia by adopting the recrystallized silicon carbide spheres as a microwave coupling agent; grinding the recrystallized silicon carbide spheres into high-activity light calcined magnesia powder by the coupling agent while burning and decomposing the magnesite into the light calcined magnesia, and efficiently recycling a high-concentration CO2 gas generated by decomposing magnesium carbonate at low cost. Resources which cannot be processed by an existing process are effectively utilized; the magnesite is ground into the high-activity light calcined magnesia while being burnt and decomposed into the light calcined magnesia, so that the activity of a product is improved, the quality of the product is improved, the crushing link is omitted, the process is simplified, and the production process is easy to control. By adopting the method of heating and burning the magnesite through nonfuel combustion, high-efficiency and low-cost recovery of CO2 is achieved and the environmental pollution is reduced.