A modified DIA type multi-anvil apparatus was installed in the Department of Earth Sciences, National Cheng Kung University, Taiwan. This modified DIA multi-anvil system is used with a hydraulic press that generates loads of up to 1000 tons and is the first multi-anvil press installed for geoscience research in Taiwan. In this paper, the geometry of the high-pressure apparatus is briefly described and the pressure calibration performed in the press is reported. The thermal behaviors of various pressure mediums, boron-epoxy, zirconia, and mullite, are also compared. Pressure calibrations at room temperature were performed with different cell designs, paying special attention to the so called "D" factor, which is defined as the ratio of diagonal length of the cell assembly cube to the diameter of the cavity hole. For a given cell design, the sample-pressure efficiency for the three materials examined was similar. Calibrations with different cell designs showed that increasing the "D" value results in greater pressure generation efficiency. By comparing the deformation behavior at high temperatures (up to 1200°C), the semi-sintered mullite and zirconia appeared to be better pressure mediums compared to boron-epoxy.