Herein, reduced graphene oxide/tin dioxide (RGO/SnO2) binary nanocomposites were synthesized through a facile one-pot hydrothermal route by using graphene oxide as a substrate. Results of morphology observations revealed that SnO2 nanoparticles were uniformly loaded on the crumpled surface of thinly flake-like RGO. Moreover, the influence of the contents of RGO and filler loadings on the electromagnetic parameters and microwave absorption properties of RGO/SnO2 binary nanocomposites were elaborately investigated. It was found that the as-prepared binary nanocomposites with the content of RGO of 9.6 wt% exhibited superior microwave absorption properties in the X-band. Remarkably, the minimum reflection loss (RLmin) achieved -53.7 dB at 11.1 GHz and effective absorption bandwidth (EAB, RL ≤ -10 dB) reached 3.7 GHz with a thin matching thickness of merely 2.2 mm. Furthermore, the EAB could reach 14.3 GHz (89.4% of 2–18 GHz) by facilely adjusting the matching thicknesses from 1.5 to 5.0 mm, which spanned the whole Ku, X and C bands. Besides, the possible microwave absorption mechanisms of obtained binary nanocomposites were proposed. This work could be helpful for fabricating graphene-based nanocomposites as high-efficient microwave absorbers.