The invention discloses a modified aramid fiber and a processing technique thereof. The modified aramid fiber comprises an aramid fiber, a sulfuric acid solution, a sodium bicarbonate solution, dichloromethane, thionyl chloride, an MgCl2 ethanol solution, a dopamine aqueous solution, a buffer solution, absolute ethanol and deionized water. The processing technique of the modified aramid fiber includes cleaning the aramid fiber, pretreating the aramid fiber, performing acylating chlorination on the aramid fiber, treating the aramid fiber with the MgCl2 ethanol solution, and treating the aramidfiber with the dopamine aqueous solution. The interfacial properties and interfacial bonding force of the obtained modified aramid fiber are improved; the whole preparation process of the modified aramid fiber is green and environmentally friendly, and the technique is simple, easy to operate, and suitable for industrial production.