Abstract: MgO/Cu composite internal oxidation layer on Cu-Mg alloy surface was prepared by internal oxidation. The effects of internal oxidation time on the thickness,hardness and electric conductivity of internal oxidation layer as well as the microstructure were studied,and the internal oxidation thermodynamics of Cu-Mg alloy was analyzed,too. The results show that the thickness and electric conductivity of the internal oxide layer increased,the hardness was increased and then decreased with the increase of internal oxidation time. When the internal oxidation time was 10 h,the internal oxidation layer had the best comprehensive properties,the hardness was 123.3 HV and electric conductivity was 75.9 %IACS. After internal oxidation,the Mg element dissolved in Cu substrate precipitated in the shape of MgO to form internal oxidation layer,and the dispersive distribution of MgO particles was the primary reason of increasing comprehensive properties of internal oxidation layer a lot. The critical oxygen partial pressure of internal oxidation thermodynamics of Cu-Mg alloy 10-31 419/T+5.66-10-17 611/T+12.91.