In order to make the high-gain antenna have a large phase shift and can work in the THz band, a reflectarray element based on Liquid Crystals(LC) is designed to operate in the frequency range from 270 GHz to 390 GHz. When the phases of reflectarray element are calculated with a constant value of the permittivity, the elements produce a dynamic phase range above 360o in 335-345 GHz, and achieve the maximum 390o at 342 GHz. Then, in order to reduce the influence of liquid crystal inhomogeneity on the phase shifting, an accurate model of liquid crystal-based reflectarray cells is established. The accurate modeling produces a dynamic phase range above 250o in 330-338 GHz, and achieves the maximum 285o at 336 GHz. Compared with the equivalent permittivity modeling, the accurate modeling has a maximum phase error of 105o, which cannot be ignored in the reconfigurable reflectarray antennas design.