To achieve accurate dielectric constant measurement of liquid and powder materials in the millimeter-wave band, this paper proposes a measurement method based on corrugated transmission lines. A dedicated test system was built using a customized polytetrafluoroethylene (PTFE) container and matched with vector network analysis technology for experimental testing. The Gated-Reflect-Line (GRL) calibration technique was adopted to mitigate measurement errors arising from multiple signal reflections and scattering between the container structure and the test samples. Following calibration, liquid or powder samples were loaded into the container, and the reflection S-parameters captured by a vector network analyzer were utilized to calculate the sample dielectric constant. Solid PTFE was tested as a standard sample to verify the feasibility and reliability of the established test system. Further experiments were conducted on quartz powder and dimethyl synthetic silicone oil within the frequency range of 75～110 GHz. The test results show that the maximum deviation of measured data from the average value is merely 5%, which verifies the superior accuracy of the proposed method. This study offers a crucial technical reference for millimeter-wave dielectric constant measurement of liquid and powder materials, supporting technical development in food processing, biomedicine and other related fields.