A preparation method of stalactite-like macroporous activated carbon, characterized in that it comprises the following steps: The activated carbon precursor is weighed and placed in a ball mill with a rotating speed of 200 r/min ~ 1200 r/min and milled for 15min ~ 2h; Then, the ball milled activated carbon precursor is pressed into flakes, and a heat conductive substrate is set on each side of the activated carbon precursor respectively to make the activated carbon precursor being placed between the two sheets of the heat conductive substrates; After weighing the high-temperature self-ignition agent and pressing it into flakes, it is placed on the outer surface of the heat conductive substrate; After weighing the low-temperature combustion-supporting agent and compressing it into flakes, it is placed on the outer surface of the above-mentioned high-temperature self-ignition agent, so that the raw materials form a sandwich structure of low-temperature combustion-supporting agent → high-temperature self-ignition agent → heat conductive substrate → activated carbon precursor in the order from the outside to the inside; The sandwich structure is heated to 120 °C ~ 200 °C in a closed argon, nitrogen or vacuum atmosphere, and the low-temperature combustion supporting agent is ignited by the ambient temperature; Meanwhile, the low-temperature combustion-supporting agent instantly generates a temperature of 1000°C or above to ignite the high-temperature self-ignition combustion-supporting agent; Therefore, the local temperature of activated carbon precursor on the heat conductive substrate is made above 1000 °C; When the activation is completed, the stalactite-like large activated carbon is obtained on the heat conductive substrate after cooling to the room temperature; In step, the activated carbon precursor is activated carbon and potassium hydroxide, and the mass ratio of the activated carbon and potassium hydroxide is 1:3.1~7.9; In step, the high-temperature self-ignition agent is iron powder and oxidant, and the mass ratio of iron powder and oxidant is 70~88:12~30; In step, the low-temperature combustion-supporting agent is zirconium and barium chromate, and the mass ratio of the zirconium to barium chromate is 3~4:6~7, characterized in that: the mass ratio of the low-temperature combustion-supporting agent, the high-temperature self-ignition agent, the precursor of activated carbon and the heat conductive substrate is 0.3~1.5: 8~15:1: 0.5~1. The activated carbon precursor is weighed and placed in a ball mill with a rotating speed of 200 r/min ~ 1200 r/min and milled for 15min ~ 2h; Then, the ball milled activated carbon precursor is pressed into flakes, and a heat conductive substrate is set on each side of the activated carbon precursor respectively to make the activated carbon precursor being placed between the two sheets of the heat conductive substrates; After weighing the high-temperature self-ignition agent and pressing it into flakes, it is placed on the outer surface of the heat conductive substrate; After weighing the low-temperature combustion-supporting agent and compressing it into flakes, it is placed on the outer surface of the above-mentioned high-temperature self-ignition agent, so that the raw materials form a sandwich structure of low-temperature combustion-supporting agent → high-temperature self-ignition agent → heat conductive substrate → activated carbon precursor in the order from the outside to the inside; The sandwich structure is heated to 120 °C ~ 200 °C in a closed argon, nitrogen or vacuum atmosphere, and the low-temperature combustion supporting agent is ignited by the ambient temperature; Meanwhile, the low-temperature combustion-supporting agent instantly generates a temperature of 1000°C or above to ignite the high-temperature self-ignition combustion-supporting agent; Therefore, the local temperature of activated carbon precursor on the heat conductive substrate is made above 1000 °C; When the activation is completed, the stalactite-like large activated carbon is obtained on the heat conductive substrate after cooling to the room temperature; In step, the activated carbon precursor is activated carbon and potassium hydroxide, and the mass ratio of the activated carbon and potassium hydroxide is 1:3.1~7.9; In step, the high-temperature self-ignition agent is iron powder and oxidant, and the mass ratio of iron powder and oxidant is 70~88:12~30; In step, the low-temperature combustion-supporting agent is zirconium and barium chromate, and the mass ratio of the zirconium to barium chromate is 3~4:6~7, characterized in that: the mass ratio of the low-temperature combustion-supporting agent, the high-temperature self-ignition agent, the precursor of activated carbon and the heat conductive substrate is 0.3~1.5: 8~15:1: 0.5~1.