Transformers are the key elements of power transformer, contributing a significant amount of carbon emissions. Transformer energy-saving and carbon reduction are crucial for the overall energy-saving and carbon reduction efforts of the power grid. The development of conductive materials with high electric conductivity for transformers has attracted much attention. Graphene-copper composites, with their high electric and thermal conductivity properties, are regarded as promising materials acting as conductive material using in transformer. However, up to date, the graphene-copper composites developed in laboratories are mainly in the form of sheet samples, mechanical and heating treatments will be conducted to produce suitable transformer electromagnetic wires. The mechanical and heat treatment may affect the micro-structure and electric performances of graphene-copper composites. In this study, mechanical treatment,i.e. drawing process, and heat treatment (annealing) were performed. The micro-structure of graphene-copper composites were observed by scanning electron microscope technique. It shows that the annealing temperature has a significant effect on the conductivity of the graphene-copper composites.