The invention discloses a riser heating and insulating agent, which comprises the following components in percentage by weight: 5 to 35 percent of Al, 10 to 25 percent of AlN, 3 to 20 percent of low-carbon graphite, 5 to 25 percent of magnesia-alumina spinel, 5 to 15 percent of quartz, 10 to 30 percent of ferric oxide powder, 5 to 20 percent of corundum, 5 to 10 percent of organosilicon phlogopite, and 1 to 10 percent of MgO; and the riser heating and insulating agent is prepared by the following processes: crushing, pulverizing, mixing, pelletizing, drying, and the like. The riser heating and insulating agent has double effects of heating and insulating, and has good insulating effect. Because the riser heating and insulating agent has a granular appearance, dust and smoke are not generated in the using process, and the environment is not polluted. Due to the adoption of the low-carbon graphite, castings do not have carburizing phenomenon, and the molten steel is not polluted. The riser heating and insulating agent is particularly applied to open risers of low carbon steel large-scale steel castings and stainless steel castings with the weight of over 80 tons.