Abstract: GH750 as domestically developed is a new type nickel base super-alloy for the super-heater/reheater tube to be used for the 700℃advanced ultra-supercritical boiler.The microstructure and the properties of GH750 alloy are studied here in the paper.As a result it is revealed that the super-alloy GH750 consists of austenitic matrix with strengthened phase γ', and trace MC and M₂₃C₆as distributed in the grain and at the grain boundary, and has excellent mechanical properties, including both high room temperature strength and elevated-temperature strength, and fine plasticity.The super-alloy also has remarkable hi-temperature stress-rupture, i.e., the 760℃/10⁵h stress-rupture strength∧100 MPa.And after long term ageing at 700~850℃, the alloy still exhibits microstructure stability, and no harmful phases are precipitated.In case of a long term ageing as up to 10 000 h, room temperature tensile property of the alloy is just slightly changed, while its impact toughness trends to be stable immediately after going down for a short time.