Abstract: A meta-surface based high efficiency pyramid horn feed is studied. By placing impedance meta-surfaces on the inner boundary of a metallic pyramid horn, an excellent and novel high efficiency feed is obtained. First, it is shown that the surface impedance is greatly modulated by the meta-surface, and that the meta-surface exhibits different impedance characteristics with respect to TE polarized and TM polarized waves. When a proper impedance is achieved, the inner boundary of the horn could support balanced hybrid mode, so as to reach rotationally-symmetric radiation beam. Then a Ku-band meta-surface feed is designed and fabricated, and the feed radiation pattern shows excellent performance. Finally, the feed is used to illuminate a 1.25 m Ku band ring-focused reflector antenna. The measured radiation patterns show great performances. Compared with the corrugated horn feed used in the reflector antenna, the meta-surface feed can achieve similar electrical performance. Meanwhile, the meta-surface feed shows obvious advantages in size, weight and cost.