The present invention relates to a surface-modified aramid fiber and a method for preparing the same. The method includes the following steps: modifying an aramid fiber having amino groups and carboxyl groups on the surface with siloxane γ-glycidoxypropyltrimethoxysilane to obtain a silicon methoxylated aramid fiber; reacting same with a cerium oxide coated with polydopamine modified chaotic boron nitride to obtain a surface-modified aramid fiber. The cerium oxide coated with polydopamine modified chaotic boron nitride has high ultraviolet absorption, and has extremely low catalytic activity, avoiding the damage to a fiber structure by photocatalysis during radiation, being an effective, safe and highly-efficient ultraviolet absorber. The surface-modified aramid fiber provided in the present invention has an ultraviolet-resistant function, high surface activity, good thermal performance, and better mechanical performance, providing excellent overall performance, and having higher utilization value. The method is simple and controllable, being suitable for large scale production.