The invention discloses a production process and a production device for co-producing light-burned MgO and Mg(OH)2 through a suspension kiln. The device comprises a raw material bin, a four-stage cyclone preheater, a decomposing furnace, a cyclone separator, a fluidifying and cooling bed, a hydration reaction tower, a finished product collecting and dust collector, a finished product bin and the like. After a magnesium carbonate powder material is sintered, an MgO clinker is obtained; after gas-solid separation, the MgO clinker is fed into the fluidifying and cooling bed through a switching gate so as to be cooled, and a light-burned MgO finished product can be prepared, or the MgO clinker is fed into the hydration reaction tower through the switching gate so as to be subjected to hydration reaction with distilled water, and an Mg(OH)2 finished product can be prepared. According to the production process and the production device for co-producing the light-burned MgO and the Mg(OH)2 through the suspension kiln provided by the invention, the characteristic of single product of an existing light-burned MgO roasting device is changed, and a technological process of high-temperature sintered MgO is changed through the switching gate of the device, so that without additionally arranging the production device, the aims of co-producing the light-burned MgO and the Mg(OH)2 at the sametime can be realized, the equipment utilization ratio is effectively improved, the energy is saved, and the production cost is reduced.