High-gain antennas play an important role in long-range wireless communication systems like radar, satellite communication, and space exploration. In such applications, Microstrip array antennas and phased array antennas require complicated feeding networks to realize beamforming and directional radiation, which increases the complexity of antenna design as well as the cost. In contrast, reflective metasurface and transmissive metasurface have high gain property with low cost due to easy fabrication . Compared with reflective, transmissive metasurface offers several advantages such as no aperture blockage from the feed source and less sensitivity to fabricating tolerances . And planar transmissive metasurface shows miniaturized size and lighter weight than traditional three-dimensional (3-D) lens antennas .Despite various advantages, normal transmissive metasurface usually suffers from limited bandwidth. In this submission, a transmissive metasurface with wide gain bandwidth is proposed. The used element is realized by a four-layer rectangular slot, showing wide phase-shifting coverage and low transmission loss within a broad bandwidth. By decreasing the design frequency of the transmission elements, the realized gain of the metasurface becomes flatter. Based on low-cost PCB technology, the metasurface with the dimension of 204 mm × 204 mm is designed and fabricated. The measured results are agreed with the simulated ones well, showing good radiation characteristics with a measured gain of 28.2 dBi at 18 GHz and aperture efficiency of 35.1%. Bandwidths of 26.4% for 1-dB gain and 47.9% for 3-dB gain are achieved as well.