The invention discloses a large-diameter high-strength heat-resistant magnesium alloy thick-wall cylindrical workpiece forming process, which comprises the steps of smelting in a big furnace, semi-continuous casting, homogenizing annealing, variable-temperature multi-directional forging, mechanical hole drilling, ring rolling formation and aging treatment, wherein the variable-temperature multi-directional forging is performed on an oil press, an ingot blank is preserved for 6-10h at 500-530DEG C before forging, downwards pressing speed is kept to 200-400mm/min, upsetting pass rolling reduction is kept to 30-40 percent, drawing pass rolling reduction is kept to 5-10 percent, the ingot blank is preserved for 3-5h at 480-500DEG C before the ring rolling formation, the rolling deformation is kept to 60-80 percent and the thick-wall cylindrical workpiece with outer diameter of 700-1100mm, wall thickness of 50-100mm and height of 300-700mm can be rolled. The thick-wall cylindrical workpiece with high strength and high heat resistance rolled by adopting the process disclosed by the invention has the advantages that the height-direction and tangent tensile strength at 200DEG C is more than or equal to 330MPa and the elongation is more than or equal to 8 percent.