In this paper, two improved methods are proposed for determining the complex permittivity of the powder materials from 1 to 18 GHz. Unlike the measurements of solid materials in a two-port coaxial line, two Teflon annular spacers are used to house the powder materials. One method is to obtain the scattering parameters at the reference plane of the powder materials using an improved TRL calibration method, then reconstruct the complex permittivity based on the traditional transmission-line method. The other method is based on the measurements of the scattering parameters of two different length coaxial lines, which only loaded with two Teflon annular spacers or partially loaded with powder materials housed by two Teflon annular spacers. Those two methods are particularly suitable for a small amount of powder materials. Finally the results of the measurements of two powder materials: loess and thin sand are shown, compared with the results measured by Agilent’s 85070E dielectric probe kit.