The invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a preparation method of a three-dimensional porous carbon aerogel material. The preparation methodcomprises the following steps: (1) adding melamine and triethanolamine into a formaldehyde aqueous solution to prepare a melamine-formaldehyde prepolymer, (2) adding lignin into water, firstly adjusting the pH value to fully dissolve the lignin, and then adjusting the pH value to separate out the lignin in the form of nanoparticles, (3) uniformly mixing hydrophilic silicon dioxide with the solutions obtained in the previous two steps, (4) slowly adding methylbenzene into the solution obtained in the step (3) to obtain emulsion, polymerizing the emulsion into hard gel, and soaking the hard gelin ethanol to replace an inner phase, and (5) sintering at high temperature, etching off silicon dioxide by using hydrofluoric acid, and drying. The method is simple, the production cost is low, andthe prepared carbon aerogel material has a three-dimensional network and a hierarchical pore structure, is applied to a lithium-sulfur battery positive electrode, can realize sulfur fixation and catalytic action while enhancing sulfur conductivity, realizes high sulfur load, can greatly improve the cycling stability, rate capability and coulombic efficiency of the lithium-sulfur battery positive electrode, and has relatively high practical application value.