Graphene-polypyrrole nanocomposites (GPN) were synthesized by in situ chemical oxidation polymerization using FeCl3 as an oxidant. The synthesis condition were optimized by changing molar ratio of surfactant content, sodium dodecylbenzene sulfonate (SDS)/monomer, and wt% graphene/monomer. The conductivity of resultant nanocomposites reached by 3.589 S/cm under the condition of 20% molar ratio SDS/monomer and 5wt% graphene/monomer. Nanocomposites were characterized by SEM, FTIR-Raman and TGA. The microwave absorbing performance of GPN were studied in X band microwave frequency (8.2-12.4 GHz). The absorbing ability was found near by 90% at the bandwidth of 4.2GHz at the thickness of 5mm absorber.