A nanostructured solid solution catalyst CeZrK/rGO for soot oxidation in catalyzed diesel particulate filter was synthesized using the dipping method. The reduced graphene oxide (rGO) was used as the catalyst carrier, and CeO₂, ZrO₂, and K₂O were mixed with the molar ratio of 5:1:1, 5:2:2 and 5:3:3, which were referred to as Ce₅Zr₁K₁/rGO, Ce₅Zr₂K₂/rGO, and Ce₅Zr₃K₃/rGO, respectively. The structure, morphology and catalytic activity of the CeZrK/rGO nanocomposites were thoroughly investigated and the results show that the CeZrK/rGO nanocomposites have nanoscale pore structure (36.1–36.9 nm), high-dispersion quality, large specific surface area (117.2–152.4 m²/g), small crystallite size (6.7–8.3 nm), abundant oxygen vacancies and superior redox capacity. The 50% soot conversion temperatures of Ce₅Zr₁K₁/rGO, Ce₅Zr₂K₂/rGO, and Ce₅Zr₃K₃/rGO under tight contact condition were decreased to 352 °C, 339 °C and 358 °C respectively. The high catalytic activity of CeZrK/rGO nanocomposites can be ascribed to the following factors: the doping of Zr and K ions causes the nanocrystalline phase formation in CeZrK solid solutions, reduces the crystallite size, generates abundant oxygen vacancies and improves redox capacity; the rGO as a carrier provides a large specific surface area, thereby improving the contact between soot and catalyst.