The invention relates to a high-smoke suppression and high-oxygen index phenolic aldehyde fire-proof heat-preserving board and a preparation method thereof and belongs to the technical field of a building fire-proof material. The high-smoke suppression and high-oxygen index phenolic aldehyde fire-proof heat-preserving board comprises the following components in parts by mass: 100 parts of phenolic resin, 10 to 20 parts of expansive fire retardant, 5 to 10 parts of liquid fire retardant, 5 to 8 parts of coal ash, 1 to 2 parts of tiny silicon powder, 1 to 2 parts of magnesium hydroxide, 5 to 7 parts of foaming agent, 5 to 7 parts of foam stabilizer and 20 to 30 parts of curing agent. The preparation method of the high-smoke suppression and high-oxygen index phenolic aldehyde fire-proof heat-preserving board comprises the following steps of 1) preparing a mixed slurry, i.e. (1) optionally selecting a formula, (2) mixing the phenolic resin and the liquid fire retardant, (3) mixing the expansive fire retardant, the hollow coal ash, the magnesium hydroxide and the tiny silicon powder, and adding the mixture into the mixed liquid, (4) adding the foaming agent and the foam stabilizer, and uniformly stirring the materials, and (5) adding the curing agent, stirring the materials, and filling the mixture into a die; and 2) molding and curing to obtain the fire-proof heat-preserving board. The fire-proof heat-preserving board has the advantages of convenience in construction, good fire resistance, low water absorption per volume, capability of meeting the requirements of high smoke suppression and high oxygen index of inner and outer wall heat-preserving boards, and the like.