The invention discloses a high-specific-strength porous carbon/carbon composite material and a preparation method thereof, belonging to the technical field of preparation of carbon/carbon (C/C) composite materials. The preparation method comprises the following steps: uniformly mixing phenolic resin, ethylene glycol and a curing agent according to a mass ratio of (10-15): (11-16): (1-2) under stirring to prepare a precursor solution, then soaking a carbon fiber preform in the precursor solution, carrying out curing at a temperature in a range of 120-250 DEG C, then carrying out heating to 1000DEG C at a rate of 5-10 DEG C/min, and carrying out multi-stage heat preservation to obtain the low-density high-specific-strength carbon/carbon composite material. According to the invention, the carbon/carbon composite material, of which the matrix carbon is of a bead chain reticular porous structure, is prepared by adding a pore-forming agent and the curing agent; the preparation method has the characteristics of simple process, short period, low cost and the like; and the prepared carbon/carbon composite material has the advantages of high specific strength, uniform pore structure and thelike.