We propose an ultra-thin Huygens lens with high focusing efficiency and robustness that is composed of a unit cell with a pair of C-shaped split-ring resonators (CSRRs). Compared with the single-layer CSRR lens, the focusing efficiency of the Huygens metasurface lens improves 90% at the best focal lengths and three times at the central frequency. Our device has robustness against geometrical parameters, such as the difference of the opening angle, the mismatch of the opening angle, and the mismatch of the radius, which reduces the manufacturing difficulty. The Huygens lens has unprecedented potential for real-time, quick, electromagnetic wave processing such as holography, beam steering/splitter, imaging, and launcher control.