In this study, two kinds of materials such as C12000 and C26000 copper alloys are used to do micro-upsetting experiment and micro-tensile experiment. It can be found that the size effects of micro-metal forming in C12000 agree with the description in that had published papers. However, C26000 alloy has high matrix strength and significant fine grain strengthening result in it appears different size effects of micro-metal forming. Therefore, it has made deep explanation on this problem and hopes it can provide a general solution and know-why for most of micrometal forming processes.