Abstract: This report reviewed the relationship between structures or properties and gas pressure for high Tc superconductor and rare earth magnetic materials. It is indicated that with the changes of oxygen pressure (or nitrogen pressure),the structures of the materials will be changed and it will result in obvious changes of superconducting and magnetic properties. In case of equilibrium state the oxygen pressure of YBCO system of sintering temperature was up to about 10MPa and the nitrogen pressure of Re-Fe-N system reached ~10MPa. A dense material manufactured under the condition of high gas pressure may have excellent properties.