Terahertz wireless communications promises to satisfy the future high-capacity demand. However, practical system for terahertz wireless communications faces many challenges. Among them, the communications distance is a crucial problem due to serious propagation loss. Here we demonstrate a 338.7 GHz wireless link based on the cesium Rydberg atoms in a room-temperature vapor cell. The minimum detectable electric field of 132 ± 13µV /cm (9.72 s detection) is realized in our system. With this atomic receiver, the phase-sensitive conversion of amplitude-modulated or frequencymodulated terahertz waves into optical signals is performed to realize the wireless communications with 8-state phaseshift-keying. The experimental results show that the atomic receiver has many advantages due to its quantum properties. Especially, the communications distance has the potential to be over 18 km. Furthermore, the atomic receiver can be used in the terahertz wireless-fiber link to directly convert the wireless signals into optical signals. Our work provide the new path to future terahertz wireless communications.