A reinforcing geotextile mat and an embankment method using the same. The mat comprises support member for supporting backfilled soil at one end or both ends of the mat. The support member comprises a horizontal support section for supporting the backfilled soil in a vertical direction; a vertical support section for supporting the backfilled soil in a horizontal direction; and an inclined support section defined with openings through which the backfilling soil passes and inclinedly embedded in the backfilled soil. The method comprises the steps of positioning a reinforcing geotextile mat on the ground or hardened embankment soil; inserting external support members in horizontal, vertical and inclined receiving portions of the mat; and backfilling horizontal, vertical and inclined support sections of the mat with soil, and then placing and hardening embankment soil on the mat. These steps are implemented one or more times.