The invention discloses an efficient and energy-saving heavy-magnesium water pyrolysis method. The efficient and energy-saving heavy-magnesium water pyrolysis method comprises the following steps: atomizing heavy-magnesium water by virtue of an atomizing device, enabling heavy-magnesium water to be in contact with high-temperature hot wind, mixing, heating and decomposing, wherein atomized heavy-magnesium water is in counter current trend with high-temperature hot wind; after adequate pyrolysis reaction, finishing gas-liquid separation in a separator, carrying out solid-liquid separation to obtain solid basic magnesium carbonate, and drying, so as to obtain pure-white high-bulkiness basic magnesium carbonate. The efficient and energy-saving heavy-magnesium water pyrolysis method has the advantages that the technical process is short, the production is continuous and smooth, cleaning is omitted, the working cycle is long, the production operation is easy, the production cost is low, equipment is simple, the fixed investment is low, an excellent operation effect is achieved in a pilot plant, and the method has industrial operation conditions.