The invention provides a modified aramid fiber pulp with an average length of 5-8 mm, wherein the modified aramid fiber pulp is a modified aramid fiber pulp containing an imidazole ionic liquid. The invention further provides a preparation method of the modified aramid fiber pulp, wherein mainly steam blasting treatment, imidazole ionic liquid spraying treatment, fluidized bed airflow mill dry grinding and other processes are performed to prepare the modified aramid fiber pulp, the method has characteristics of short process, low energy consumption, no solvent and environment protection, and the prepared modified aramid fiber pulp has characteristics of high fibrillation degree, rich hairiness and large specific surface area. According to the present invention, with the application of the modified aramid fiber pulp as the reinforcing material to produce the brake lining and other friction materials, the strength, the toughness and the heat resistance of the brake lining are improved, the preparation formula does not contain asbestos, and the green environment protection advantage is provided.