The invention discloses a multielement-reinforced heat-resistant magnesium alloy and a manufacturing method thereof. The multielement-reinforced heat-resistant magnesium alloy is prepared from the following raw materials in parts by weight: 1000 parts of magnesium, 65-85 parts of aluminum, 5-8 parts of zinc, 10-30 parts of yttrium, 1.5-5 parts of manganese, 5-15 parts of neodymium, 3-4 parts of cerium, 1-4 parts of calcium, 0.4-1 part of strontium, 0.1-0.5 part of silicon, 3-6 parts of silver and 10-40 parts of boron carbide. The manufacturing method comprises the following steps: carrying out acid washing, drying and preoxidation on the boron carbide, preheating the materials, smelting the magnesium and aluminum while introducing protective gas, adding an aluminum-manganese alloy and a pure zinc ingot to carry out alloying, adding an aluminum-silver alloy, a magnesium-silicon alloy, a magnesium-yttrium alloy, a magnesium-cerium alloy, a magnesium-neodymium alloy, a magnesium-calcium alloy and a magnesium-strontium alloy, smelting, adding the boron carbide particles for reinforcement, carrying out gas refinement on the melt by using argon, carrying out extrusion casting, and finally, carrying out solid solution aging treatment to obtain the heat-resistant magnesium alloy finished product. The magnesium alloy has excellent comprehensive properties under high-temperature conditions.