The voltage characteristics of a half-wavelength transmission (HWLT) system lack mechanism explanation and systematic summary. In this paper, both the steady-state and fault voltage characteristics are analyzed and explained based on the wave process method. An analysis model is established for HWLT lines and wave propagation equations with different terminal conditions are deduced. For steady-state conditions, voltage profiles along HWLT lines are depicted and partial overvoltage occurs when there is an overload or low-power factor. In addition, fault voltage characteristics are analyzed under load-rejection or short-circuit conditions. The series resonance overvoltage will happen when short-circuit faults occur at certain positions and its peak value is influenced by grid strength or fault type. Furthermore, a refined transmission line model is presented to consider non-ideal factors and simulation results demonstrate that geomorphic conditions and electromagnetic environments influence line voltage characteristics to a certain extent.