The invention provides an activated carbon fiber-ferroferric oxide composite material and a preparation method thereof. A viscose felt is placed in a phosphoric acid solution for predetermined time, the processed felt is taken out and is dried, and then the dried felt is placed in a muffle furnace filled with inert gas to carry out first-time carbonization, so that viscose-based activated carbon fiber felt is obtained; the viscose-based activated carbon fiber felt is immersed in a ferric chloride solution in a constant-temperature water bath kettle; after the processed felt is taken out and isdried, the dried felt is placed in a glucose solution, and the processed felt is taken out and then is dried to obtain an iron-containing activated carbon fiber felt; and the iron-containing activated carbon fiber felt is placed in the muffle furnace filled with inert gas to carry out second-time carbonization, so that an activated carbon fiber- ferroferric oxide composite material is obtained. The activated carbon fiber-ferroferric oxide composite material has the following beneficial effects: firstly, the experimental conditions are simple and used raw materials are cheap; secondly, the activated carbon fiber yield is high; and thirdly, with the in-situ reduction method, the ferroferric oxide is loaded on the activated carbon fiber felt, so that the bonding firmness is high; and the mass of the composite material is low and the broadband absorbing effect is realized.