Highly efficient electromagnetic wave (EW) absorbers that are lightweight and have strong absorption properties remain a great challenge to produce and are sought after by researchers. In this paper, Co@Fe@Cu hollow nanospheres were synthesized using a simple electroless plating method based on a galvanic cell reaction, and composites of reduced graphene oxide (RGO)/Co@Fe@Cu hollow nanospheres were obtained successfully by mechanically stirring the reaction. The EW absorbing properties of the prepared materials were investigated. The results show that the composite RGO/Co@Fe@Cu hollow nanospheres with the loading of only 5% exhibit excellent EW absorbing properties compared with RGO and Co@Fe@Cu hollow nanospheres alone. The paraffin-added RGO/Co@Fe@Cu hollow nanospheres possess a minimal reflection loss of -49.71 dB and a maximum bandwidth of 6 GHz at only a 5 wt% additive concentration with a thickness of 2.1 mm. Considering the above advantages, the composite RGO/Co@Fe@Cu hollow nanospheres can be used as a new highly efficient, ultra-lightweight, antioxidation and broadband absorbing material for electromagnetic waves.