The invention discloses an expanding anti-flaming charring agent containing a nickel synergistic element and a preparation method thereof, relates to the technical field of an expanding anti-flaming agent and specifically relates to the expanding anti-flaming charring agent containing the nickel synergistic element. The nickel-containing expanding anti-flaming charring agent contains 4-5wt% of nickel element. The preparation method comprises the following steps: firstly, dissolving a nickel source in a phosphoric acid solution, thereby preparing a nickel phosphate precursor solution; adding the precursor solution into an esterification reaction system of trihydroxy ethyl isocyanurate and terephthalic acid drop by drop; causing the reaction system to pre-react for 6-10h at 150 DEG C-180 DEG C; adding the precursor solution into the reaction system, and then causing the new system to react for 2h under the original reaction temperature; and after the reaction ending, grinding the cooled product and using deionized water for filtering and washing for several times, thereby acquiring the expanding anti-flaming charring agent containing the nickel synergistic element. According to the invention, a nickel-containing synergistic agent is combined with an efficient charring agent, so that the anti-flaming efficiency of the expanding anti-flaming agent is increased, and meanwhile, the step of independently adding the nickel-containing synergistic agent is avoided and the application and the popularization of the nickel-containing synergistic technique in practical production are benefited.