A graphene/bismuth nanocomposite film-modified pencil graphite electrode was quickly prepared for the simultaneous analysis of cadmium and lead heavy metal ions by square wave anodic stripping voltammetry. The pencil graphite electrode's surface was directly modified from graphite to graphene with cyclic voltammetry method in a single step by performing potential cycling between -0.9 and -1.4 V in 0.2 mol L-1 NaOH modifying solution. A linear relationship between peak current and concentration was obtained in the range between 5-100 mu g L-1 for both Cd2+ and Pb2+, with detection limits of 0.12 mu g L-1 for Cd2+ and 0.29 mu gL(-1) for Pb2+. The developed electrode with the proposed method has been applied to a Canadian-certified reference water sample and tap water sample with reliable results. For tap water sample, the obtained results were in a good agreement with the results provided by AAS.