A Uband lefthanded metamaterial is designed and simulated to obtain the scattering parameters after the dimensions are estimated according to the transimission line theory of the lefthanded metamaterial. Furthermore, the properties of transmission and the negative electromagnetic parameters are analyzed after effective permittivity; effective permeability and refraction index are calculated by the Smith parameter retrieval method. The results show that the proposed lefthanded metamaterial structure behaviours the negative refraction characteristic while the real parts of effective permittivity and effective permeability are both negative in 48.8~59.9 GHz band. Thus, the existence of the lefthanded metamaterial in Uband is demonstrated，and it is of great reference significance to research on metamaterials in higher band.