Flame-retardant medium density fiberboard（MDF） was prepared by inorganic Magnesium-Aluminum layered double hydroxide（Mg Al-LDH） as the flame retardant. The effects of Mg Al-LDH on fire retardant and mechanical properties of the MDF were analyzed and compared with MDF made by melamine phosphate（MP） as the fire retardant. The results showed that the fire retardant and smoke suppression effects were more effective when the Mg Al-LDH levels increased. When the Mg Al-LDH level was 15%, the heat release effect was similar to MDF made with 10% MP but showed superior smoke prevention. The more Mg Al-LDH that was used, the weaker became the mechanical properties of the MDF. However, when 10% Mg Al-LDH was used, the mechanical properties of the MDF still met the GB/T 11718-2009 National Standard requirements for ordinary MDF products.