The invention belongs to the technical field of heat insulating material preparation and relates to a porous composite pearlite heat insulating material. The heat insulating material is made of the following raw materials in percent by weight: 15-60 percent of pearlite particles, 30-70 percent of bentonite, 2-10 percent of polycrystalline aluminum oxide fiber, 0-1 percent of anti-cracking fiber, 1-10 percent of polyacrylamide, 5-20 percent of toluene diisocynate (TDI-, 100-65) and 5-10 percent of water repellent, wherein the diameter of the pearlite particles is no more than 6mm; the weight percentage of aluminum oxide in the polycrystalline aluminum oxide fiber is 30-90 percent; the anti-cracking fiber comprises polypropylene and the length of the anti-cracking fiber is 1-10cm; and the molecular weight of the polyacrylamide is 3-12 million. The porous composite pearlite heat insulating material has the advantages that the production process is simple, the scientificity is good, the production cost is low, the raw materials are easy to obtain, the heat insulating performance of a product is good, the weight is light and the popularization and application are facilitated.